Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/19/17
Area Forecast Discussion...Updated
National Weather Service Billings MT
850 PM MST Mon Dec 18 2017
.UPDATE...
Winds have been slowly decreasing from Livingston to Nye to Big
Timber. Have not had warning criteria for quite a while at
Livingston, and winds were now safely below advisory criteria.
Cold front was pushing south through the forecast area this
evening, and winds should continue to decrease. Will cancel the
wind highlights.
Band of light rain/snow was stretching from around Harlowton to
near Ashland, and has been slowly sinking south with the front.
Models have not done a very good job at all with the band, as they
have it placed way too far north. Latest RAP and GFS have finally
caught up with it, and linger this band in the current position
through the early overnight hours, then lift it north. Have raised
PoPs to account for this. Precipitation has been on the light
side within this band, but as the cold air sinks in, could
actually see some light accumulations with it, especially over
along the northern tier of zones. Have raised snow amounts a bit.
TWH
&&
.SHORT TERM...valid for Tue and Wed...
Strong winds continue along the western foothills this afternoon
with recent gusts to 60 mph being observed at Livingston and Nye.
Winds will gradually decrease through the evening as a cold front
drops into the area, but will remain somewhat breezy near
Livingston and Nye overnight. Have extended the High Wind Warning
for the Livingston area and Beartooth foothills through 9pm.
The aforementioned cold front will drop south into the area this
evening bringing increasing chances for rain/snow, transitioning
over to all snow tonight as colder air works into the area. Best
chances for precipitation will be over the SW mountains, as well
as for areas generally north of a Harlowton to Roundup to Miles
City line. A few inches of snow can be expected on south and west
facing slopes in the Beartooth/Absaroka mountains overnight, with
an inch or less of snow for northern areas, as the best forcing
and precipitation chances are across northern Montana.
Weak shortwave ridging tries to build into the area on Tuesday
with snow showers continuing over the southwest mountains and far
northern areas. Surface pressure gradients tighten once again
Tuesday evening/night with strong winds possible for the Upper
Yellowstone and Upper Stillwater valleys. Will need to monitor for
any potential wind highlites. Heading into Wednesday, the next
disturbance arrives in the form of a deepening trough and
associated upper low. An associated cold front is expected to dive
south during the day ushering in colder temperatures along with
increasing snow chances. Depending on how quickly we cool across
the area, roads may experience some melting snow initially, before
freezing and accumulating with snow. Models are somewhat out of
phase with the timing of the front, however, there is general
agreement on much of the area seeing an inch or two of snow, with
better chances for accumulating snow over the foothills and
mountains. Will hopefully have a better feel on snow
accumulations over the next day or so as models come into better
agreement. Winds will increase Wednesday evening and night as a
surface low departs the area, bringing the potential for blowing
and drifting snow. High temperatures will range from the 30s and
40s for Tuesday and Wednesday. Wednesday`s highs will likely be
reached early in the day with temperatures falling throughout the
afternoon. Lows in the 20s can be expected tonight and Tuesday
night, with temperatures down into the single digits Wednesday
night. STP
.LONG TERM...valid for Thu...Fri...Sat...Sun...Mon...
Did not need to make any large changes to the going extended
forecast. Both the GEFS and ECMWF ensembles showed increasing
spread with the pattern during the period. Noted that on Monday,
the GEFS plumes had temperature spreads around 60 degrees for the
forecast area. The deterministic 12Z models were not that
different from their previous runs and were actually fairly
similar with their forecasts through much of the period. There
were some differences in temperature details beginning on Sunday.
Still had high confidence in much colder than normal temperatures
for most of the period with a good chance of snow Friday into
Saturday.
Trough moves out of the area on Thursday with snow ending over SE
MT by afternoon with little accumulation. Temperatures will reach
the teens and 20s. The next system dives SE into the area Thu.
night and Friday, ushering in much colder air and snow with the
cold front. Chances for snow will spread SE across the area Thu.
night and continue across the region on Friday. The best chances
for snow will be over the NE and N upslope areas, where at least
several inches of snow are expected. Highs will reach only the
teens. Chances for snow will decrease through Saturday as the
upper trough swings SE of the area. Expect highs in the single
digits to teens on Saturday. Windy conditions will create areas of
blowing snow Fri. through Saturday. Decent pressure gradient will
create windy conditions Sat. night from Harlowton to Big Timber to
Livingston. Northerly flow will be over the region on Sunday with
drier conditions. Blended guidance kept highs in the single digits
to teens. Kept forecast mostly dry through Monday, although ECMWF
brought more energy down in the N flow with some QPF. Surface
gradient again supported windy conditions in the W Sunday night
and Monday. Arthur
&&
.AVIATION...
Southwest winds will remain gusty tonight near KLVM and K6S0, but
gusts should be near or below 45 kt. Rain and snow showers are
expected over areas of southern MT overnight into Tuesday. MVFR
CIGS are possible overnight over SE MT. IFR CIGS are expected at
BIL overnight into Tuesday and are possible at SHR late tonight
into Tuesday morning due to upslope flow in those areas. Mountains
will be obscured tonight into Tuesday. RMS
&&
.PRELIMINARY POINT TEMP/POPS...
Tue Wed Thu Fri Sat Sun Mon
-----------------------------------------------------------
BIL 029/039 029/034 008/025 016/019 005/014 003/017 004/017
62/S 17/S 62/S 34/S 32/S 21/N 11/N
LVM 037/045 033/035 010/025 018/018 003/012 002/015 004/020
32/O 16/O 51/U 45/S 32/S 21/N 11/N
HDN 026/043 027/037 006/025 015/019 007/016 003/017 001/018
62/S 16/S 72/S 35/S 33/S 32/S 11/B
MLS 026/036 023/033 007/021 013/019 006/014 001/014 901/015
62/S 26/S 62/S 23/S 22/S 21/B 11/B
4BQ 026/042 026/041 008/023 011/020 004/015 001/016 901/015
61/E 12/O 73/S 13/S 32/S 31/B 11/B
BHK 022/034 021/031 003/017 009/015 002/011 903/009 904/012
41/E 34/S 72/S 23/S 32/S 21/B 11/B
SHR 024/043 026/045 009/024 009/020 003/014 000/017 902/019
21/B 13/R 83/S 24/S 32/S 22/S 11/B
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
950 PM CST Mon Dec 18 2017
.DISCUSSION...
Cleaned up the hourly grids based on latest trends. Main issue
remains the fog, especially over inland parts of the area. Vsbys
towards the coast have improved a bit, but HRRR does suggest they
could lower again this evening/overnight. So for now, the dense
fog advisory will remain in effect, but will need to monitor
things over the next several hours.
&&
.PREVIOUS DISCUSSION... /Issued 626 PM CST Mon Dec 18 2017/
DISCUSSION...
Visibilities crashed quickly across the area within the last hour
or so, prompting many changes to the forecast. Numerous observing
stations are reporting vsbys less than a mile with a handful at
one quarter of a mile or less. As a result, a dense fog advisory
was issued for much of the area, and will likely need to expand
into Webb/LaSalle counties at some point. In addition, the marine
dense fog advisory is also in effect now with many locations along
the water at a mile or less. Both headlines will run concurrently
through 15z. Complicating factor will be how rain chances evolve.
One area should continue to push northeast out of the area within
the next hour or two. Another round of showers may move out of
Mexico later tonight and impact locations across western parts of
the area. This could result in vsbys bouncing around a bit, but
overall trends should still support dense fog. Will continue to
monitor.
Please see 18z aviation section below.
AVIATION...
IFR/LIFR conditions developed quickly this evening as very low
stratus and dense fog blanket much of the area. These conditions
should persist for much of the night into Tuesday morning. Rain
will be possible at times, but was only confident enough to
include VCSH remarks in the forecast. Southerly winds will pick up
mid to late morning on Tuesday, which will help vsbys gradually
improve. Some gusts between 20 and 25 knots will be possible in
the afternoon at ALI/CRP/VCT with lighter winds expected at LRD.
Despite the fog mixing out by late morning, low clouds should
hang on into the afternoon hours and remain in the IFR/MVFR range.
PREVIOUS DISCUSSION... /Issued 350 PM CST Mon Dec 18 2017/
SHORT TERM (Tonight through Tuesday night)...
Mixture of stratiform/convective precipitation over the CWA today
likely associated with the upper jet streak and isentropic
lift/low condensation pressure deficits (300K at least), and the
isolated/scattered shower/thunderstorm activity over the MSA
linked to the coastal trough. Confident that the upper
disturbance/500-mb low will enter TX overnight, with associated
synoptic scale lift over the CWA after 12z Tuesday. Expect the
coastal trough to move onshore and over the ERN CWA early Tuesday
in response to the foregoing upper disturbance. The combination
of surface/upper forcing and sufficient moisture will contribute
to scattered convection/areas of rainfall Tuesday. With respect to
thunderstorms, surface-based activity should be restricted to the
ERN CWA near the surface trough Tuesday afternoon. Elevated
thunderstorms may occur over the WRN CWA. Drier conditions
expected from west to east Tuesday night as the upper system moves
east.
MARINE (Tonight through Tuesday night)...
NAM/GFS/RAP deterministic consistent with the development of
onshore flow developing overnight over all of the MSA along with
increasing moisture advection. NAM deterministic predicts surface
dew points to exceed SST values (per 17 December 2017 1800 UTC
SPoRT SST Composite and current select SST values at Port
Aransas/Port Lavaca/Baffin Bay) after 06z Tuesday. Issued a dense
fog advisory for the bays and nearshore waters for the 06-15z
Tuesday period.
LONG TERM (Wednesday through Monday)...
The sun should finally make an appearance across the area on
Wednesday as moisture decreases behind a boundary that pushes
through Tuesday night. High temperatures warm into the mid and upper
70s for Wednesday and a bit further Thursday, into the upper 70s and
lower 80s. And that`s where the simple part of the forecast ends.
Upper level trough will dig into the western US late week, and will
bring active weather back to the region. Details of the forecast
remain unclear as wild swings continue to occur from run to run,
especially with the outlook from Sunday onward. What we do expect at
this time... A warm front lifts northward on Thursday bringing an
increase in moisture and possibly some showers as early as Thursday
afternoon in the east. Marine fog would also become a concern with
very warm moist air flowing over the cool nearshore waters and bays.
A cold front then follows on Friday bringing a substantial drop in
temps, though timing is not clear yet as to whether we have a chance
to warm in the morning before the front or not. Behind the front
temperatures drop back to the 50s or lower 60s for highs Saturday
and lows in the 40s. Will also see a chance for rain Friday,
especially in the east where better moisture pooling is.
Another stronger front looks to move through at some point between
Sunday morning and Tuesday morning with more of an arctic. airmass.
Obviously this makes for a tricky holiday forecast. Models have
trended a bit earlier with this front, closer to the Sunday time
frame, but still too much variation to put much stock into the
timing. At this point, going to go with a cool day on Christmas,
with just a slight chance of rain in the east. Stay tuned for
updates!
&&
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 63 76 57 75 58 / 40 30 20 10 10
Victoria 62 76 54 73 54 / 50 60 40 10 10
Laredo 59 70 52 75 58 / 40 20 10 0 0
Alice 61 76 55 78 57 / 40 30 10 10 10
Rockport 64 72 59 71 60 / 40 30 30 10 10
Cotulla 57 70 48 76 54 / 50 50 10 0 0
Kingsville 62 78 56 78 58 / 30 20 20 10 10
Navy Corpus 65 73 61 72 62 / 30 20 30 10 10
&&
.CRP WATCHES/WARNINGS/ADVISORIES...
TX...Dense Fog Advisory until 9 AM CST Tuesday For the following
zones: Aransas...Bee...Calhoun...Duval...Goliad...Jim
Wells...Kleberg...Live Oak...McMullen...Nueces...Refugio...
San Patricio...Victoria.
GM...Dense Fog Advisory until 9 AM CST Tuesday For the following
zones: Bays and Waterways from Baffin Bay to Port Aransas...
Bays and Waterways from Port Aransas to Port O`Connor...
Coastal waters from Baffin Bay to Port Aransas out 20 NM...
Coastal waters from Port Aransas to Matagorda Ship Channel
out 20 NM.
&&
$$
TB/78...SHORT TERM
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
620 PM CST Mon Dec 18 2017
.UPDATE... /DENSE FOG ADVISORY ISSUED/
With decreasing precipitation rates forecast by the recent runs of
the HRRR for the rest of tonight, the likelihood of an extended
period for possible dense fog could continue through the early
morning hours. The advisory is now expanded to cover all counties
along and SE of an Eagle Pass to Bandera to Burnet line. Only other
minor change was to remove thunder from the evening grids for areas
generally along/north of I-10.
&&
.AVIATION... /00Z TAFS/
VLIFR CIGs/VSBYs will become more widespread this evening into the
overnight. Have these conditions at KAUS, KSAT, KSSF through midday
on Tuesday. However, as RA becomes more widespread with ISOLD TSRA
late tonight into morning, CIGs/VSBYs may improve slightly and have
this mentioned in PROB30s for TSRA from 19/14Z-20Z. Out west at KDRT,
CIGs/VSBYs will lower to LIFR, possibly VLIFR overnight as -RA
develops there. As drier air filters into our area in wake of the
upper level trough mentioned below moves across, RA/TSRA will move
off to the east with CIGs/VSBYs becoming VFR, at KDRT early in the
afternoon and KAUS, KSAT, KSSF late afternoon into early evening.
VRBL winds of 5 KTs will prevail tonight into Tuesday, then become
westerly 5 to 10 KTs during the afternoon into evening.
&&
.PREV DISCUSSION... /ISSUED 243 PM CST Mon Dec 18 2017/
SHORT TERM (Tonight through Tuesday Night)...
Light winds at the surface and a stout inversion up to 850 mb has
kept moisture trapped in the boundary layer all day today with foggy
conditions still being reported. With little change expected for the
rest of the afternoon and tonight, the fog should remain in place and
expand in coverage again through the overnight hours. Temperatures
have been kept in check a bit because of this with current values in
the middle to upper 50s. A large upper trough axis near the AZ/NM
border continues to slowly push east and as it does so widespread
forcing for ascent will overspread the region mainly after 06z and
will provide a widespread coverage of showers and isolated
thunderstorm activity for the eastern two-thirds of the CWA. In the
mean-time, ascent in the southwest flow aloft is leading to light
rain across the southeastern third of the CWA and points to the
southeast this afternoon.
The overnight showers and storms will continue to move to the
northeast in the morning hours before the bulk of the activity moves
out of the CWA around mid-day. Later in the afternoon, the Pacific
front associated with the upper low will be moving through the area.
This will provide surface focus for convection which will allow for
the redevelopment of some shower and thunderstorm activity tomorrow
afternoon. There will be continued upper support as the main forcing
from the upper low arrives to Texas. The trough will be in the
process of transitioning from a positive tilt to becoming negatively
tilted which will help increase upward motions. However, the best
lift will be in North Texas as the center of the low is progged to
move through the Red River Valley. With the aforementioned conditions
this should be sufficient enough for some scattered showers and
storms are a broken line of convection along the frontal boundary as
it moves from west to east tomorrow afternoon. The convective storm
environment shows CAPE values around 1000 J/kg and 0-6 km shear
values in excess of 60 knots. With this setup, can`t rule out a
strong to marginally severe storm across our eastern counties, but
the instability looks to to be the limiting factor. In addition, a
mid-level dry slot may also help limit convective updrafts. All
activity will be east of the region by the evening hours tomorrow.
Highs tomorrow will be in the 70s in the southeastern CWA where some
heating will occur in the warm-sector ahead of the front and lows
Tuesday night will bottom out in the 40s and lower 50s.
LONG TERM (Wednesday through Monday)...
Wednesday and Thursday will likely be the warmest days of the week
behind the Pacific front with highs in the 70s. There could be some
warm air advection showers across the Coastal Plains in the afternoon
Thursday and will mention a 20 PoP there. On Friday, another large
trough axis will push through the Central Conus and another stronger
front will arrive to the area Friday morning. A slight chance to
chance of showers are expected with the higher PoPs across the
eastern counties. Highs Friday will likely be right before the front
arrives with temperatures dropping into the 40s and 50s behind it.
The pattern will remain progressive and not expecting any precip
beyond Friday evening with this system. The ECMWF shows return flow
by Saturday ahead of the next reinforcing shot of colder air but the
GFS keeps weak north flow in place. Regardless, temperatures on
Saturday will likely top out in the 50s. The stronger front arrives
Sunday morning and will bring with it a brief chance of showers and a
strong bite of cold air. Highs on Christmas Eve will likely struggle
to get out of the 40s for most of the area and highs on Christmas
Day will likely be in the 30s and lower 40s. Christmas morning will
feel like it as well with lows possibly in the 20s and 30s. Have your
coats ready this Christmas season.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 56 69 49 75 51 / 80 100 30 0 0
Austin Bergstrom Intl Airport 56 70 48 74 49 / 80 100 30 0 0
New Braunfels Muni Airport 56 70 48 75 50 / 80 90 20 0 0
Burnet Muni Airport 55 63 45 72 49 / 60 100 20 0 0
Del Rio Intl Airport 52 69 44 75 49 / 50 30 0 0 0
Georgetown Muni Airport 55 67 48 72 50 / 70 100 30 0 0
Hondo Muni Airport 55 68 44 76 48 / 70 70 10 0 0
San Marcos Muni Airport 56 70 48 74 49 / 80 90 20 0 0
La Grange - Fayette Regional 60 71 52 73 51 / 70 90 70 0 0
San Antonio Intl Airport 57 69 49 75 52 / 80 80 10 0 0
Stinson Muni Airport 57 70 48 75 51 / 80 80 10 0 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until midnight CST tonight for the following
counties: Bastrop...Bexar...Blanco...Burnet...Caldwell...Comal...
Guadalupe...Hays...Kendall...Lee...Travis...Williamson.
&&
$$
Mesoscale/Aviation...04
Synoptic/Grids...Oaks
Public Service/Data Collection...YB
Area Forecast Discussion
National Weather Service Grand Rapids MI
946 PM EST Mon Dec 18 2017
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 311 PM EST Mon Dec 18 2017
The mixed precipitation affecting the area earlier will push out of
the area by this evening. A good deal of cloud cover will remain,
but we will see a gradual clearing of the clouds through Tuesday
afternoon. Temperatures will stay mild through Tuesday as many see
lows tonight above freezing, and highs on Tuesday well into the 40s.
A system well north of the area could clip areas north of I-96
Wednesday night into Thursday. A more significant system is likely
to affect the area with multiple precipitation types from Thursday
night through Saturday. Much colder air will then filter in over the
area over the Christmas weekend.
&&
.UPDATE...
Issued at 946 PM EST Mon Dec 18 2017
The overall forecast is on track however it seems the clouds,
especially the lower clouds have moved out and due to drier air
forecast to come in at low to mid levels. This is shown nicely by
time sections in BUFKIT of the GFS, RAP and HRRR models as well as
the HRRR layered cloud forecast image in AWIPS and GFE Aviation.
It can be seen looking at the IR image loops too. So our forecast
now calls for partial clearing overnight.
There is enough wind in the boundary layer tonight to keep the air
mixed so I do not think less clouds will allow the temperatures to
drop significantly more than were in our previous forecast.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 311 PM EST Mon Dec 18 2017
Fairly quiet weather by December standards expected for the short
term. We will be timing out pcpn/cloud cover at the beginning, and
then timing in some light snow chances for Wed night. Nothing looks
significant through Wed night.
The last of the rain in the area extends from near South Haven to
Lansing as of 1930z. This is likely at the tail end of the upper
wave that is almost through the area. All of the pcpn is occurring
where the sfc temps and atmosphere are warm enough for rain. Low
clouds shroud the remainder of the area. Some clearing breaks are
trying to work their way in from Srn Lake Michigan. The high dew
points over the snowpack will resist the clearing initially.
The strengthening winds tonight are expected to blow the low clouds
out eventually, leaving mainly mid clouds into Tue morning. Models
are in good agreement that the area should clear out for Tue
afternoon, minus some high clouds. Good mixing with sunshine, and
warmer air moving in from the SW should help temps well into the 40s
on Tue. Temps will cool down Tue night and Wed as a dry back door
cold front drops down Tue evening.
Our next chance for precipitation will come Wed night across the nrn
half of the area in the form of some light snow. The aforementioned
front from Tue night will try to push NE as the system emerges from
the Rockies. Mid level fgen/moisture return will develop at the
leading edge of the warmer air aloft. This will be overcoming an
initially dry atmosphere, so amounts will be limited Wed night.
.LONG TERM...(Thursday through Monday)
Issued at 311 PM EST Mon Dec 18 2017
The main challenge deals with the potential impacts from the storm
system that tracks through the region Thursday through Friday.
Models are coming into agreement in showing a band of snow impacting
northern parts of my cwa. The latest GFS shows more than 6
inches...while the High Res Euro keeps the values under 3 inches. An
elevated warm layer shows up as well...and that increases the risk
for a period of freezing rain. Either way some impacts look
possible in that timeframe...so will increase POPs...mention some
accumulations and add a risk for a period of freezing rain mainly
north of a Hart to Big Rapids to Mount Pleasant line. We also
added the potential into the Hazardous Weather Outlook.
The arctic air starts to flow in behind this departing storm
Saturday and into early next week. There are some indications that
a wave of low pressure will form along the frontal zone off to the
east. This may support a period of snow around Sunday if the wave
does develop.
Good confidence on the arrival a very cold airmass early next week
as the persistent northwest flow continues. Will keep the mention
of snow showers going and feature well below normal temperatures.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 540 PM EST Mon Dec 18 2017
Like last night, the low clouds that prevail now are expected to
break up this evening and all taf sites should have several hours
of VFR cigs. Also like last night later in the evening the low
clouds come back as the atmosphere cools off as it typically does
at night causing the boundary layer to saturate (hence low clouds
form). I am thinking around 06z for this to happen. Also unlike
last night we have a warm front trying to come through tonight.
Once that does come through skies will really clear. That should
be in the 09z time frame. There is to much wind for much fog
tonight so that should not really be an issue.
I have put low level wind shear in all of the overnight TAFS as by
03z we have 40-45 knots at 1000 ft AGL creating around 20 knots
of shear that will be around most of the rest of the night.
Tuesday we will be between the warm front and the cold front. This
will result in mostly clear skies with a west wind from 10 to 20
knots. The cold front comes through around 06z on Wednesday that
will bring some lower clouds into the picture then.
&&
.MARINE...
Issued at 311 PM EST Mon Dec 18 2017
We will be extending the Small Craft Advisory out through Wednesday
afternoon due to the persistent winds and waves expected through
then. Winds will come up this afternoon in the wake of the wave
moving through. This gradient will last into Wed before relaxing a
bit. We can not rule out gales occurring, especially up north. The
likely scenario is that we max out advisory conditions.
&&
.HYDROLOGY...
Issued at 311 PM EST Mon Dec 18 2017
The Looking Glass River at Eagle has shown consistent improvement in
the last couple of days. It is now within banks and the advisory has
been dropped. There no remaining advisories in Southwest Lower.
Ice continues to be observed on multiple rivers. Gauges at sites
such as Whitehall (WHTM4) and Portland (PORM4) are still reflecting
some erratic behavior due to the affects of the ice. Coordination
with Ionia County officials did verify that the Portland site is
elevated near bankfull in locations where land is lower, but largely
not affecting anything otherwise. The White River at Whitehall
remains within banks with the gauge periodically sending in
erroneous reports above flood stage. We will continue to monitor
each of the locations through the week.
Forecast precipitation amounts for the upcoming week have not
changed much. Milder air, snowmelt and rain/snow later in the week
could lead to additional rises. This may actually be beneficial by
giving a bigger push to lose ice, clearing some of it downstream
through the end of the week. Flooding is not expected at this time,
but rivers will continue to be monitored for ice jam potential.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 4 PM EST Wednesday for LMZ844>849.
&&
$$
UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...JAM
MARINE...NJJ
Area Forecast Discussion
National Weather Service Huntsville AL
914 PM CST Mon Dec 18 2017
.NEAR TERM...(Tonight)
Issued at 914 PM CST Mon Dec 18 2017
After a cloudy and foggy start earlier today, the sun actually broke
through, helping to warm temperatures across the Tennessee Valley
into the upper 50s and lower 60s - notably warmer than it has been in
the recent past, and "normal" highs of around 52 degrees this time of
year. 9 PM temperatures have cooled into the mid 40s to around 50.
The above noted clear skies (still mostly clear over the Tennessee
Valley east of the I-65 corridor) have allowed for radiational
cooling and the formation of fog. The older GOES-13 low cloud/fog
view nicely indicated the areas of fog especially in and near river
valleys; as well as newly commissioned GOES-16 (now GOES-East)
night-time microphysics view.
Dense fog has already affected parts or NE Alabama and Southern
Middle Tennessee, with surface visibilities at or below 1/4 of a
mile. The temperatures/dewpoint spread at the Huntsville Int`l and
Decatur airports was staying near zero, and reports of ground fog
have been received in and near the larger cities.
Given the fog affecting the eastern half of the area, went ahead with
a Dense Fog Advisory for the forecast areas through 9 AM Wed AM. The
movement of higher altitude cirrus over the western areas may slow
down fog development there, but still think some could occur, before
lower clouds arrive towards dawn Wed AM. New output from the NAM, as
well as the HRRR and RAP held off on precipitation affecting the
forecast area till after 6 AM, so did likewise in recent grid
updates.
.SHORT TERM...(Tuesday through Thursday)
Issued at 253 PM CST Mon Dec 18 2017
Attention will quickly turn to another upper-level shortwave and its
associated heavy rainfall and thunderstorm potential from midday
Tuesday through Wednesday afternoon. Most locations will remain dry
through the morning as cloud cover begins to increase with the
advancing front. The aforementioned boundary will slowly creep
northward into the Tennessee Valley by 18z and continue to lift NE
through the afternoon. The associated lift from this weak frontal
boundary will help to generate a clusters of numerous showers and
possibly a few isolated to scattered thunderstorms, thanks to some
weak instability. This front will also help to advect richer Gulf
moisture into the area as PWATs climb to 1.5 inches or so by 00z
Wednesday. Total QPF forecast for Tuesday is expected to be 1/2 to
3/4 of an inch, with heavier rains to come Tuesday Night into
Wednesday.
As alluded to, chances for precipitation will continue to increase
through the evening hours and overnight period. An mid-level
shortwave will become negatively tilted as it tracks into the Mid
South late Tuesday evening. In response, a strong 70 kt LLJ will
ramp up from Central Mississippi into Northern Alabama late Tuesday
night into Wednesday morning. Most of the Tennessee Valley will be
placed in a favorable location for lift, the front entrance region of
the jet. The combination of deep moisture and strong synoptic and
mesoscale lift will result in numerous to widespread heavy showers
late Tuesday Night through Wednesday morning, before a cold front
sweeps through by midday/early afternoon. Current model projections
show roughly 2 to 3 inches of rain, mainly occurring between 18z
Tuesday and 18z Wednesday, with the highest totals occurring over NW
Alabama. While we have been fairly dry of late, this much rainfall
could lead to some runoff and localized areal flooding issues in the
usual flood prone areas. This certainly warrants a mention in the HWO
and at this point, a need for a Hydrologic Outlook to address
flooding concerns for this event and another potential system late
this week.
In addition to the flood threat, there will be some limited elevated
instability to generate some scattered to isolated thunderstorms,
especially Wednesday morning as the LLJ maxes out over Northern
Alabama. Given that the "better" instability does not develop until
later in day when the best lift has exited the area, think the
primary mode will be rain showers or at the very least subsevere
thunderstorms. However, due to the magnitude of this LLJ and a warm
front nearby, cannot totally rule out a strong storm developing
Wednesday morning (with gusty winds being the main threat), and have
maintained a mention of this in the HWO.
The cold front will pass through the area Wednesday afternoon,
bringing in some drier air and an end to precipitation by the
evening. The end result will be a dry night and then day on
Thursday, with the best shot for sunshine we`ve seen in almost a
week. Mild temperatures will continue as highs in the 60s and lows
in the 50s can be expected for most of this period.
.LONG TERM...(Wednesday night through Sunday)
Issued at 253 PM CST Mon Dec 18 2017
The extended portion of the forecast begins Friday with an area of
low pressure having developed across portions of MO and the Ern
Great Plains. This feature is in response to a deepening H5 trof
across much of the Central CONUS/Intermountain W, with a cold front
stretching W/SW into Central/Southern portions of TX.
Let me preface much of the extended forecast with these two words:
it depends. There has been very little run-to-run model continuity
over the past few days, and recently some models that were favoring
warm/wet solutions have now flip-flopped to cold/dry (and vice
versa). So, I say "it depends" depending on which model you favor
for what time period as to what the forecast could potentially end
up being. As of this forecast package, I`m leaning towards
warmer/wetter through the weekend (and perhaps Christmas - maybe),
with a more cold/dry turn for the time period after that. Then
again, all of this could flip-flop again by this time tomorrow, so
stay tuned for forecast updates over the next few days, as I`m sure
there will be plenty of them between now and the Christmas holiday!
The extended forecast can be broken up into 3 sections: Rain, Severe
Wx (low risk), and Uncertainty. More details below:
RAIN: While much of Thursday will be dry for much of the area,
increasing Srly winds ahead of the approaching upper trof will allow
for decent isentropic lift to occur, and likely for showers to
develop/blossom by daybreak Friday morning. This will be the first
`round` of rainfall, of sorts, to affect the region, with the brunt
of the precipitation arriving/developing later in the day closer to
the later afternoon/early evening hours. A few disturbances will
ride up/over the front oriented SW to NE across the Southeast, which
will set the stage for several rounds of moderate to heavy rainfall
through midday Saturday. Storm-total rainfall amounts upwards of 3.5-
4" are possible across NW portions of the area, dwindling down to
around 1.5-2" for SErn portions of the area. This in and of itself
is a lot of rainfall, but following so quickly on the rainfall from
earlier in the week, I`m thinking that we`ll have at least a few
issues from either areal flooding, river flooding, or more likely,
both. We`ll see how much rainfall occurs with the midweek system to
give a better idea on exactly what we can expect with these kinds of
rainfall totals to end the week. Please refer to the Hydrologic
Outlook for more general information about the flooding
possibilities for this time period, and as always, if a warning is
issued for your location later in the week or over the weekend.
SEVERE WX (low risk): Aside from all the talk about the heavy
rainfall that we`re expecting, there`s also the potential (albeit a
low risk at this point in time) for some strong to severe storms on
Friday as the cold front pushes across the area, depending on your
model of choice. For example, the GFS has a high in the low 70s
Friday, whereas the ECMWF is 10 degrees cooler in the lower 60s.
You`re going to have different values of instability with those sfc
based temps. As with other systems that have moved across the region
earlier this Fall, we`ve seen little in the way of instability, and
a lot in the way of shear. This system isn`t too different with its
parameters, but this time, there is a little sfc based instability
that may be realized, which may pose a wind threat more than
anything. With the model flip-flopping of recent days, I don`t feel
comfortable believing a model output 100% to include the "T-word" at
the moment, but right now, it`s on the lower end of likelihood of
occurring. 850mb winds will increase to 50kts during the aftn, with
925mb winds around 40-45kts. This should translate to a windy day
outside of any tstorm activity, with sustained winds around 15-20mph
(with higher gusts likely). As the cold front approaches the area
later in the day Friday, wind gusts up to 60mph may occur along the
line of showers and storms along the front. IF we were to see
something rotate, there`d be a brief window around 00Z Saturday for
this to happen, when the best shear intersects with the little
instability that we have in place.
That said, there MAY be a chance for something Friday morning with
the first round of showers blossoming across the area. If the warm
front isn`t well N of the area, anything that crosses over that
boundary may enhance what little rotation is there. So, I`m not
saying that we`ll have 2 rounds of tornadoes, but there is a tiny
possibility that something may try to rotate at 2 points during the
day. As of this model run. Which may change tomorrow. Stay tuned for
more on that.
UNCERTAINTY: As if that`s not enough, there is a lot of uncertainty
in the forecast from Christmas Day onward across the Tennessee
Valley. The big question is how much of the Arctic air bottled up to
the NW of the CWFA will make it here, and how much moisture will
linger over us as well. If you believe the latest run of the GFS,
we`ll have snow in our higher elevations on Christmas night. The
ECMWF isn`t much different, but the big problem with QPF spit out by
the models compared to sounding analysis shows big differences
between the two. Whereas the models try to produce light snow for
us, the soundings are really dry in the lower and mid levels, so
even IF something was to develop and fall, it`d evaporate before it
hit the ground. This all relates back to the big uncertainty that
exists in this portion of the forecast right now. The upper levels
that far out in the extended look to have W/SW flow aloft, and
you`re just not going to get crazy cold without something plunging
this far S (and sticking around more than a day). Long story short,
I didn`t make many changes to Christmas and beyond thanks to all the
model flip-flopping, but it looks as if we`ll at least get a couple
of chances to have cooler than normal weather next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 547 PM CST Mon Dec 18 2017
Good flying weather this early evening, will deteriorate in the late
evening and overnight, as patchy fog forms across the region. Some of
this fog could become locally dense, with visibilities falling below
1/2 of a mile at times. Did not take this pessimistic view in the TAF
this issuance, but do have MVFR VIS and CIGS in the 1000-2000ft AGL
developing after midnight. A storm system forming over the NW Gulf
will move to the ENE, and bring more lower clouds and good shower
chances after daybreak Wed. CIG/VIS values in the MVFR range should
be reduced to IFR by the early afternoon. LIFR CIG/VIS reductions are
possible in the mid/late afternoon. An isolated to scattered t-storm
cannot be totally ruled out Wed afternoon too, but did not include
given high uncertainty on convection.
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Dense Fog Advisory until 9 AM CST Tuesday for ALZ001>010-016.
TN...Dense Fog Advisory until 9 AM CST Tuesday for TNZ076-096-097.
&&
$$
NEAR TERM...RSB
SHORT TERM...AMP.24
LONG TERM...12
AVIATION...RSB
For more information please visit our website
at weather.gov/huntsville.
Area Forecast Discussion
National Weather Service Wilmington NC
939 PM EST Mon Dec 18 2017
.SYNOPSIS...
Warm and increasingly moist air ahead of an area of low pressure will
result in widespread wet weather late Tuesday night into
Wednesday night with rain and perhaps a brief rumble of thunder.
A brief cool down will occur Thursday, followed by a return to
unseasonable warmth with the risk for showers during the
weekend and perhaps on Christmas day itself.
&&
.NEAR TERM /THROUGH TUESDAY/...
As of 945 PM Monday...00Z soundings from MHX and GSO confirm
what models were showing with the depth of boundary layer
moisture being nearly ideal for fog tonight. In fact we`re
already seeing substantial drops in visibility from Florence and
Marion to Wilmington as fog is already beginning to develop. In
Florence visibility recovered back to 10 miles as soon as the
winds increased to 4 knots. Gauging how strong surface winds
will be overnight will be critical to determining how
widespread and how dense fog may become.
Latest GFS LAMP guidance indicates fog not becoming that big a
deal overnight due to winds and steadily falling dewpoints. It`s
worth noting that LAMP guidance is already badly too low with
its current-hour dewpoints, so I`m not going trust it. Among the
better initialized guidance, the HRRR shows very little fog
while the RAP and NAM show substantial fog developing in the
Cape Fear region overnight. A good nocturnal inversion is
already developing from Florence, Marion and Conway northward
despite 15-20 kt of wind at the 1000 foot height. Given this
observation, I`ll keep "areas" of fog in the forecast tonight
and highlight the Cape Fear region for special concern as this
is where boundary layer moisture should remain richest.
Other changes to the forecast were generally minor. Discussion
from 300 PM follows...
A weak frontal boundary draped across SC into coastal NC will
continue to support weak lift advecting some sprinkles and
clouds across the area. A mid to upper level ridge extending up
from S Florida and broad trough to the north will maintain a
basically zonal or westerly flow aloft. Some energy in the mid
to upper levels will ride across the area later today, at which
time the models show a slight increase in lift and potential for
light pcp through the early eve hours. Otherwise, SW to W
return flow at the sfc and westerly flow aloft pushed temps into
the mid 60s to near 70 most places this afternoon and it will
remain mild into this eve. There is also some potential for sea
fog to develop and brush the coast primarily early on as winds
along the coast have backed to the S to SW and increased
slightly into early this evening before the winds veer to a more
westerly direction which should help keep it away from the
coast overnight.
Any sprinkles will dissipate into late eve and there will be a
decent amount of clearing overnight. Mild and damp weather will
continue though, with overnight lows in the mid 40s to lower 50s and
dewpoint temps close to that. This shallow moisture will lead to
areas of fog developing across the area. Moisture profiles actually
show the greatest potential for sea fog across coastal locations
heading into early this eve with fog inland developing later, around
08Z. The deep westerly flow aloft should mix down and break up the
fog leaving increasing sunshine through Tues aftn and temps reaching
into the 70s.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM Monday...Moisture will be streaming into the area
Tuesday night in deep layer westerly flow. Low level winds will be
largely parallel to isotherms at first limiting ascent. This changes
rapidly Wednesday morning however as a flat wave of low pressure
approaches from the west. Despite a fairly meager backing in the
warm sector the winds strengthen on the north side of the baroclinic
zone resulting in significant frontogenesis. Moderate rain should
break out west to east and include most of the area. The bulk of the
rain may fall north of our CWA and far southern zones will be hard-
pressed to get meaningful rain amounts given the current anticipated
storm track, but models have been uncertain of this and thus so is
QPF. Have also left thunder out of the forecast not only based upon
forecast model soundings but with the support of SPC SWODY3. The
specter of convection though does further erode QPF confidence. Dry
air then sweeps in from the north Wednesday night as the wedge
asserts itself behind the departing low.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 300 PM Monday...In the wake of a cold front, high pressure
will build south and wedge into the area Thu and Thu night,
briefly knocking temps down to values more typical for late
December. In fact Thu may be the only day in which temps are
below normal this forecast period as clouds get trapped beneath
a subsidence inversion. A weak coastal trough is expected to
develop offshore Thu night and Fri with the wedge breaking down
and high pressure shifting offshore Fri. A deep trough in the
middle of the nation is expected to be reinforced, remaining
upstream of the eastern Carolinas through Christmas day. This
will bring a return to a strong and deep SW flow. Thu and Fri
should be dry. A rather weak surface cold front to the west is
expected to drift into the area during the weekend and will
likely get hung up in close proximity given the prevailing flow.
As a consequence, the holiday weekend is looking unsettled and
unseasonably warm. The risk for showers will be on the increase
Fri night. Will carry chance POPs for the weekend and Mon, but
higher POPs could be in store for at least portions of the area
with later forecasts.
High temps will be in the 50s Thu and 60s for the remainder of
the period. Highs may reach 70 over the weekend. The coolest
night will be Thu night, mainly 40s although a few inland spots
could dip into the upper 30s. Lows will be mainly in the 50s for
the weekend. The unseasonable warmth may eventually result in
the development of sea fog. Dewpoint recovery coupled with a
favorable wind direction will make sea fog development most
probable this weekend.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
As of 23Z...A weak stationary boundary continues to sit to our
south with some of the moisture overriding it resulting in some
light showers across the region with no impact on aviation. Main
concern for the overnight period will be models indicating some
low stratus clouds and fog with IFR/LIFR across the terminals
after 08z. Could see some sea fog near the coast but w winds
should keep the sea fog from moving across KMYR and KCRE.
Conditions improve after 13z all terminals with VFR conditions
through 20/00z.
Extended Outlook... Unsettled weather Tuesday night through
Thursday morning as a near stationary front moves in and out of
the region. Possible showers Saturday.
&&
.MARINE...
NEAR TERM /THROUGH TUESDAY/...
As of 715 PM Monday...6-7 PM buoy observations near Cape Fear
showed seas about half a foot higher than predicted, mainly due
to a pulse of stronger westerly winds over the past few hours
with gusts 20-25 knots out at the Frying Pan Shoals buoy. These
winds should diminish over the next few hours with directions
remaining westerly. Radar shows only a few very light showers or
sprinkles south of Cape Fear, which should dissipate entirely
before midnight. Dewpoints remain quite high for this time of
year and we`ll continue to monitor for the potential of sea fog
developing. Discussion from 300 PM follows...
Quiet marine conditions although there may be some sea fog in
the mix. A light SW return flow will veer to the west through
tonight around 10 kts. Sea fog may develop late this afternoon
in a moist and warm SW flow with dewpoint temps up around 60 and
water temps in the 50s. Overall seas will be 1-2 feet with
perhaps a few three footers into tonight as winds pick up
slightly.
SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM Monday...West to southwesterly flow in place
Tuesday night with high pressure centered over Bahamas and
Florida. A wave of low pressure will approach from the west
along a sagging frontal boundary and this will tighten the
gradient and lead to considerable backing of the flow Wednesday.
Late in the day the boundary will sag across most of the NC
zones turning winds all the way to the NE briefly before turning
back to E. This all hinges upon the yet uncertain position of
the front and so it subject to change. AS the frontal wave moves
offshore Wednesday evening a wedge of high pressure will
quickly move in and lead to a gusty NE flow that could allow
advisory-worthy seas to affect the outer portions of NC waters.
LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 300 PM Monday...In the wake of a cold front, high pressure
will briefly build south Thu and Thu night. A coastal trough
is expected to develop offshore Thu night into Fri. A deep
trough across the middle of the nation will be reinforced with
the flow across our waters shifting from NE Thu and Thu night to
E and SE Fri and finally to S and SW Fri night and Sat ahead of
a rather weak front. Small Craft Advisory conditions may linger
into Thu and this is when the strongest winds are expected this
period. Wind speeds will subside late Thu through most of Fri
and then increase to around 15 kt Fri night and Sat. The highest
seas Thu will be in the 4 to 6 ft range. Seas will subside to 3
ft Thu night and 2 ft Fri before building to 4 to 5 ft by Sat.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.
&&
$$
SYNOPSIS...RJD
NEAR TERM...TRA/RGZ
SHORT TERM...MBB
LONG TERM...RJD
AVIATION...MAC
MARINE...
Area Forecast Discussion
National Weather Service Lincoln IL
907 PM CST Mon Dec 18 2017
.UPDATE...
Issued at 905 PM CST Mon Dec 18 2017
High pressure centered to the southeast of Illinois, across the SE
states will maintain a general influence over the weather in
central Illinois tonight. Some low clouds and fog are expected to
surge northward into southern and southeast Illinois later
tonight, on southwest winds/return flow behind the high pressure.
Most of counties should escape any coverage from the low
clouds/fog, except for towards Lawrenceville based on the latest
HRRR model. The sky grids have that scenario handled ok, but we
did not introduce fog yet due to 2 other high res models keeping
fog clear of our SE counties. Will continue to monitor trends with
those weather elements. Low temps tonight will be kept warmer with
steady SW winds and warm advection flows. Lows should be in the
upper 30s.
On Tuesday, an surface trough approaching from the northwest will
pass across Illinois, with minimal impact expected. Mainly mid and
high clouds are forecast for our forecast area. Prevailing
sunshine should help temps climb well above normal, into the
low 50s north of Peoria, to the upper 50s south of I-70. Winds
will shift to the NW during the afternoon, after the surface
trough passes.
&&
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 301 PM CST Mon Dec 18 2017
Skies will continue to clear late this afternoon and skies should
be mostly clear through the night and into tomorrow. Could be some
scattered clouds around but not enough to hold temps down. Temps
overnight should remain above freezing tonight and then with
southwesterly winds tomorrow, plenty of WAA and sunshine to allow
temps to climb above 50 across the entire CWA.
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 301 PM CST Mon Dec 18 2017
A weather system is forecast to move across the southern
Mississippi valley mid week but looks like the precip should
remain south of the CWA through the period. This will bring in
some clouds and slightly cooler temps, through still above normal
for middle of Dec. As this moves east, southerly winds will return
with lots of WAA continuing ahead of the next weather system. The
next weather system will bring clouds and precip into the
northwest parts of the CWA beginning Thursday evening. The precip
should remain across the far northern portions of central IL Thur
night. Models then disagree on speed of this system and the
secondary system moving through Fri and Fri night. GFS is quickest
and Canadian is slowest. So prefer the middle ECMWF solution that
has the low pressure area of the system moving into Mich by Fri
evening. Precip is expected with this system with the highest pops
being in the eastern and southeastern part of the CWA Friday
afternoon and evening. P-type will be a mainly rain on Friday,
with a rain/snow mix in the northwest early. By afternoon, it will
be warm enough everywhere that all precip will be liquid. As the
front goes by, colder air is supposed to move into the area. With
the slower ECMWF solution, the rain will change to a mix of rain
and snow, to just all snow Friday night. Temps will be warm
ahead of the system and then get colder after the front moves
through. The timing of this colder air will determine when the
change over to snow occurs, which could be around the time the
precip is ending as well. So, currently not expecting much
accumulation.
Models differ even more for the weekend and after a brief dry
period Sat and Sat night. There might be another system for Sun
and Sun night but the GFS and ECMWF have no precip while the
Canadian has precip. Therefore, will keep low chance pops in
forecast for now. Colder than normal temps are also expected for
the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 557 PM CST Mon Dec 18 2017
VFR conditions should prevail at the terminal sites for the 00z
TAF period, with mainly mid and high clouds drifting across the
area later tonight and tomorrow. A band of low clouds and fog will
surge northward toward our counties, and possible affect areas
south of I-70, but we are not expecting that fog/low clouds to
reach the TAF sites. The NAM12 is an outlier model that brings
VLIFR clouds across the TAF sites just after sunrise tomorrow. For
now, will not acknowledge that solution, but will monitor all high
resolution guidance for any change in trends.
Winds will remain southwest around 10kt overnight, then become
more westerly tomorrow and decrease to 7-9kt as the pressure
gradient weakens. LLWS conditions tonight look to remain north of
I-74, so have not included in our 00z TAFs. Will monitor the
potential of LLWS in our area as well.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Shimon
SHORT TERM...Auten
LONG TERM...Auten
AVIATION...Shimon
Area Forecast Discussion
National Weather Service Northern Indiana
655 PM EST Mon Dec 18 2017
.SYNOPSIS...
Issued at 638 PM EST Mon Dec 18 2017
Low clouds continue to erode from west to east as drier comes in
along with high pressure. Dry air will be able to stay around the
region until the end of the week as a low pressure system
approaches from the south for Thursday night and Friday. Tuesday
lows will be in the mid to upper 30s with highs in the upper 40s
to low 50s, both above average. Wednesday will be cool again
before trending warmer for Friday. Cooler air and possibly some lake
effect snow follows for next weekend.
&&
.SHORT TERM...(This Evening through Tuesday)
Issued at 350 PM EST Mon Dec 18 2017
Focus on near term with respect to final bout of very light
rain/drizzle associated with final northern tier shortwave within
confluent split flow pattern. Despite high crossover temps/partial
clearing later tonight, sufficient mixing within boundary layer
and subtle dry air advection, to most likely preclude br formation
of any significance. This also inline with latest rap
projections. Raised temps Tue inline with latest non met
mos/upstream performance today and trend over past several days.
&&
.LONG TERM...(Tuesday Night through Monday)
Issued at 350 PM EST Mon Dec 18 2017
A few substantive changes with respect to latest blended approach.
Benign stretch through much of work week. Desert southwest system
still tracking well south with TN/gulf states cyclogenesis on Wed.
Thereafter, a very highly amplified flow regime develops with
eastern Pacific ridging/deep north central NOAM trof with slow
eastward progress. Leeside cyclogenesis late Wednesday with
northeast ejection into Western Upper Great Lakes. Blend
substantially lowered pops Fri afternoon/early Fri night and have
raised back to likely/categorical given anticipated depth to
longitudinal flow/GOMEX moisture feed. Also, EC significantly warmer
8H for diminished post frontal les production, have raised pops
significantly as muted lake effect snow parameter likely failing to
capture what should be at least a high prob, if even low qpf event.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 638 PM EST Mon Dec 18 2017
Drizzle is expected to leave the area at or just after forecast
issuance and low level stratus is moving to the east fairly
quickly with clear skies approaching in its wake. Models show
stratus lingering at FWA, but they haven`t had a decent handle on
how quickly the stratus peal-back has been occurring so will speed
that up some. Expect CIGs at SBN to continue to remain VFR
through the overnight while MVFR CIGs at FWA may take 1 to
possibly 6 hours to peal back, if model trends are right for them,
before its all the way out.
One thing to watch will be if we get some fog/BR formation. Snow pack
has diminished to a trace or less at SBN, but the ground is moist
region-wide nonetheless. Winds have diminished to between 5 and
10 kts behind the stratus layer, but could pick back up some with
a stronger low level jet just overhead. Should winds be around 10
kts for most of the night that would quell this idea for most
areas.
At any rate, for Monday, increasing sunshine should be had as high
pressure approaches from the west and drier air is around the
region. Winds will be able to decrease during the afternoon as
high pressure continues to move in and the low level jet leaves
the area.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 4 PM EST Tuesday for LMZ043-046.
&&
$$
SYNOPSIS...Roller
SHORT TERM...Murphy
LONG TERM...Murphy
AVIATION...Roller
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AREA FORECAST DISCUSSION
National Weather Service Jackson KY
629 PM EST Mon Dec 18 2017
.UPDATE...
Issued at 629 PM EST MON DEC 18 2017
With the cloud cover continuing to be stubborn out there this
evening, increased cloud cover through the rest of the night as
NAM/GFS bufkit soundings keep us cloudy all night. This will also
keep temperatures a tad milder tonight, so did increase them along
with dewpoints. Looks like the drizzle is coming to an end with
cloud heights quickly increasing.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 340 PM EST MON DEC 18 2017
20z sfc analysis shows high pressure to the south with low
pressure to the north. In this pattern the air mass has not been
able to sufficiently change enough to clear out the ample low
level moisture trapped under an inversion that is keeping the
clouds in tight. In addition, patchy fog and drizzle still plague
the area - primarily on the ridge tops. Temperatures are still
rather mild despite the clouds with readings now up in the upper
40s most places with low 50s noted in many of the valley spots.
Winds, meanwhile, continue to blow from the southwest at 5 to 10
kts.
The models are in good agreement aloft through the short term
portion of the forecast. They all depict a northern stream wave of
weak energy passing by to the north this evening while a
southwestern trough bottoms out in northern Mexico. This wave
will slowly move east into Tuesday pushing downstream ridging up
into Kentucky. However, fast flow will persist over Kentucky with
energy from the southern stream moving through the Tennessee
Valley late Tuesday and into Tuesday night. As the wave opens up
and approaches Kentucky more energy moves in by Wednesday
morning. The trend has been for this wave and its impacts to shift
further north with each run. So have followed suit with increasing
confidence. With the models in good agreement handling these key
features will favor a model blend along with a healthy lean toward
the higher resolution NAM12 and HRRR tonight and into Tuesday.
Sensible weather will feature another mild but damp night. Low
stratus and patchy drizzle/fog will continue to affect most of the
area - especially on the ridges and in the higher terrain. With
sunup on Tuesday we should see the stratus start to break up.
There are indications in the models that this would occur from
east to west. Expect a fairly warm day with only limited sunshine
on Tuesday as high clouds from the next system move in around the
same time as the low ones break up. Southwest winds will continue
to support above normal temperatures and a fair amount of
moisture in this air mass. The center of the next low pressure
system will pass to the south of Kentucky with a well defined
comma head crossing through the southern half of the CWA start
Tuesday night. Warm conditions ahead of this system will prevent
any mix concern on the leading edge - it is possible later on in
the wake of the low passing by to the south and east that more
cold air gets pulled in and we will have to look as a mixed pcpn
potential on the northern fringe of the departing rain shield
- but that is just beyond the short term portion of the forecast.
Again with the clouds and moisture tonight into Tuesday did not
deviate too far from the ShortBlend temperatures. Did raise PoPs
a notch through Tuesday morning to keep up with the drizzle
threat. Also brought the higher PoPs in quicker on Tuesday night
with that inbound southern stream low.
.LONG TERM...(Wednesday through Monday)
Issued at 320 PM EST MON DEC 18 2017
A bit of a complex forecast in store for the extended. The latest
model data is suggesting an active pattern that will feature three
periods of active weather. The first would be Wednesday and
Wednesday night, followed by Friday through early Saturday evening,
with a third active period from Sunday morning through Monday
morning. An area of low pressure is forecast to move out of the
southern Plains and across the lower Mississippi and Tennessee
valleys Wednesday and Wednesday night. This system will bring
scattered to numerous rain showers to eastern Kentucky to begin the
period. Temperatures should remain warm enough to keep any
precipitation we get in liquid form. The models have been pretty
consistent with the evolution of this system and the timing, extent,
and amounts of its associated precipitation, so confidence is pretty
good with this initial wave of rain. The second period of
precipitation is forecast for Friday through Saturday evening. The
models differ here slightly with regards to timing of the system,
with the GFS being slightly faster than the ECWMF. The forecast will
reflect a slightly modified model blend that incorporates the timing
differences mentioned above. Once again we expect temperatures to
remain warm enough to keep any precipitation with this second
weather system in liquid form.
A good deal of uncertainty comes into play with the third period of
active weather in the extended. Timing differences exist amongst the
various models, with one model having a wide swath of precipitation
moving into eastern Kentucky by early Sunday morning, while another
model has no precipitation moving into the area until Sunday evening
at the earliest. The blended model was adjusted toward the typically
reliable ECMWF model for the Sunday through Monday time frame. The
onset of precipitation on Sunday was slowed down more than what the
stand along ECMWF model was showing and slightly faster than the
blended model data had. The new forecast will show some rain and
snow making their way into our southern counties between 10 and 12Z
on Sunday, with a gradual northward progression of the mixed precip
through out the morning. By early Sunday afternoon any ongoing
precipitation should be in the form of all rain. The model data is
currently trying to producing a decent snow event for Christmas eve
night and early Christmas morning along the Ohio River, north of the
river in particular. At this time the forecast will be calling for a
mix of rain and snow for Sunday night, with mostly snow ongoing
across the area by early Monday morning. There is alot of
uncertainty in the model that far out, however, so the very end of
the extended will be taken with a grain of salt at this time.
Based on the latest model data, and trends therein, temperatures in
the extended will be well above normal across the area. Particularly
toward the end of the week, when persistent southerly and
southwesterly winds become established across the Tennessee and Ohio
valleys. These winds will set up in the region between an area of
high pressure that will be parked off the southeastern CONUS, and an
area of low pressure aloft that is currently progged to be taking
shape over the central Plains and moving eastward Thursday night
into Friday. Highs on Thursday are expected to top out from the low
50s in our far north to the upper 50s along the TN border. On Friday
conditions may be even warmer, as by then we will be firmly
entrenched in the warm sector of an approaching cyclone. Highs on
Friday may climb as high as the upper 50s and lower 60s across the
area. Temperatures will then become progressively cooler, as the
upper trough exits the area, and cooler air moves in from the north
and northwest. Sundays highs should only make it into the 40s for
most of the area.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
ISSUED AT 629 PM EST MON DEC 18 2017
A tricky aviation forecast tonight. Most locations have returned
to MVFR in the last few hours. However, it would probably be a
safe assumption that cloud heights will start to come down
overnight. The question is just how low do we go by daybreak
Tuesday. For now, going to stay close to guidance that has most
areas socked in with IFR conditions, but I could see a few
locations staying in the MVFR category. As clouds finally start to
erode on Tuesday, we will return to VFR conditions around midday.
Light southwesterly winds are expected through the period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...AR
AVIATION...KAS
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
528 PM CST Mon Dec 18 2017
.SYNOPSIS...
Issued at 405 PM CST Mon Dec 18 2017
Across the CONUS this morning, a zonal pattern was
dominant across the northern half of the country. The main features
of note this morning across the southern CONUS was a closed low over
southern Arizona and strong high pressure over the Bahamas. WV
imagery continues to indicate a large plume of Pacific moisture and
high cloudiness across the northwestern CONUS this morning. This
cloud cover has drifted east across the northern Rockies and was
entering the high plains of South Dakota and western Nebraska as of
this afternoon. Abundant tropical moisture was present from west
Texas, east to the Carolinas and Georgia. At the surface: A weak
trough of low pressure extended from eastern Wyoming into eastern
Colorado. East of this feature, a north to south aligned pressure
gradient was present across western and north central Nebraska. With
light westerly winds and partly to mostly sunny skies across western
and north central Nebraska, 3 PM CST temperatures ranged from 53 at
Gordon to 61 at Imperial.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 405 PM CST Mon Dec 18 2017
Tonight and Tuesday...Benign weather conditions will
highlight the next 24 hours across western and north central
Nebraska with no precipitation expected. Skies tonight will
generally be mostly clear with some high clouds transitioning from
north to south. For the cloud cover tonight, generally followed the
NAM12 H500 to H300 Layer RH field for clouds tonight. This seemed to
initialize the best with the invading cloud cover in the panhandle
this morning. That being said, this cloud cover will transition from
north to south overnight with clearing in the south toward day break
Tuesday. A weak cold front will drop through the Dakotas overnight
and nose into northeastern Nebraska Tuesday morning. Then the front
will stall with the core of cold air being well off to the north and
northeast of the forecast area. Lows tonight will range from the
middle 20s to the lower 30s which is well above normal for this time
of year. On Tuesday, a surface trough of low pressure will develop
from the Black Hills south into northeastern Colorado. Southerly
winds will increase in the afternoon hours for locations along and
west of highway 83. This will begin to push warmer air into
southwestern and western Nebraska from Kansas and eastern Colorado.
Highs Tuesday will range from the upper 40s across the nrn tier to
the middle 50s in far swrn Nebraska.
.LONG TERM...(Tuesday night through Monday)
Issued at 405 PM CST Mon Dec 18 2017
Tuesday night through Friday: For Tuesday night into Wednesday: The
stalled out frontal boundary across northeastern Nebraska will track
north as a warm front Tuesday night. This will allow warm air to
push into western and north central Nebraska for Wednesday. By
midday Wednesday, H85 temps will range from 7c in the northeast to
12c in the southwest. The superblend forecast initialized with highs
generally in the 50s with some highs around 60s in the far
southwest. Based on the fcst H85 temps, this may not be warm enough
and is lower than the latest MAV and MET guidance highs. Feel this
is a good start however, as the NAM and the GFS develop high clouds
Wednesday and this would hold highs back some.
Wednesday night through Friday: The main forecast concern late in
the week is the passage of an arctic cold front and the threat for
light snow or a wintry mix of precipitation Overnight Wednesday
night into Thursday. Beginning Wednesday evening, a strong arctic
cold front will track through western and north central Nebraska. By
03z Thursday, the cold front will enter northwestern Nebraska,
exiting the forecast area by 09z Thursday. Fcst soundings and cross
sections indicate a shallow wedge of warmer air just off the surface
behind the front. This shallow wedge of warm air only lasts 3 to 6
hrs behind the front. Fcst soundings INVOF of the front, as well as
cross sections taken perpendicular to the front indicate a 3 to 6
hour window for the threat for freezing pcpn immediately behind the
front. QPF`s are expected to be fairly light at a hundredth or two
INVOF the front, so will keep any mention of freezing precipitation
as freezing drizzle The threat for fzdz will be mainly east of a
line from Bassett to Ogallala. North of this line, enough mid level
moisture exists to support a seeder/feeder process and all snow. I
did go ahead and end the threat for freezing drizzle in the south by
noontime Thursday, based on BUFKIT and fcst cross section
temperatures in the NAM and GFS. As for the best chances for pcpn
Wednesday night into Thursday: Isentropic lift is strongest from the
eastern Panhandle through the sandhills into north central Nebraska.
This location doesn`t deviate much from the inherited forecast so
not much was changed for precipitation chances. As for QPF and the
amount of snow accumulations: The GFS continues to be the highest of
the bunch with the EC lower and the NAM12 indicating little if any
precipitation. Utilizing the superblend, loaded QPF`s were around
0.05 in the south to around 0.15 inches in the sandhills and
northern Nebraska. Utilizing roughly a 15 to 1 snow ratio, yielded
snowfall amounts from a half an inch in the south to 2 to 3 inches
in the sandhills and northern Nebraska. Will continue to highlight
this in the HWO as we may eventually need a winter wx advisory for
this event.
Friday night through Monday: The long range models continue to indicate
a significant Arctic intrusion over the Central United States next
weekend and depending on the amount of snow cover, we may see some
of the coldest temperatures seen for this time of year for quite
some time. We`re taking an optimistic approach with temperatures
as the forecast is only calling for up to a couple inches of snow at
most late week and next weekend. Also, there is some disagreement
between the GFS and ECMWF as to how deep and far west the brunt of
the cold air will slide. The ECMWF generally keeps minus teens at
h85 across much of the CWA through the weekend, but the GFS suggest
temperatures as cold as minus 20 to minus 30 settling across the
area Christmas Eve. So with the optimistic forecast, single digit
to teens highs are forecast with sub-zero to low single digit lows
expected through the extended. This time of the year we can see
brutally cold air masses as indicated by record lows generally of
minus 20 to minus 30 and record cold highs near or slightly below
zero, so records at this point are safe.
The northwesterly pattern aloft will force a cold front across the
forecast area ever 34-36 hours, with that, the models show some
enhancement of the surface wind. Brutally cold wind chills are
likely this weekend, especially across our north. The latest
guidance indicates readings approaching minus 20 across northern
Nebraska Saturday and Sunday morning. If this holds true, wind
chill headlines will be required.
In terms of precipitation, the broad trough centered across the
Central United States will usher some fairly significant upper
dynamics/energy across the region. But under the presence of this
Arctic intrusion, moisture will be severely lacking. This sets the
stage for the potential of a high SLR snow event, but not much
additional accumulation. Another inch or so will be possible for
some areas, but most places will see less. At this point, QG
analysis suggest the best shot at additional snow will be across our
west and southwest early Saturday with northern Nebraska under the
threat on Sunday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 528 PM CST Mon Dec 18 2017
A weak cold front, currently across srn MT and srn ND, will move
south into nrn Neb overnight. The front could become the focus for
MVFR/IFR cigs across srn SD. These cigs may drift or build south
into nrn Neb by 12z Tuesday. This would generally impact areas
along and north of highway 20 Tuesday morning. The model soundings
of the RAP and NAM show fog along the front but the SREF
indicates a better chance of MVFR cigs. VFR is expected all areas
18z-00z Tuesday afternoon.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler/Jacobs
AVIATION...CDC
Area Forecast Discussion
National Weather Service Marquette MI
531 PM EST Mon Dec 18 2017
.SHORT TERM...(This evening through Tuesday)
Issued at 416 PM EST MON DEC 18 2017
WV imagery and RAP analysis indicated mainly a zonal mid/upper level
flow through the northern CONUS and southern Canada with a shortwave
trough over nrn Ontario. At the surface, sw flow prevailed ahead of
a trough moving through the plains. Radars indicated an area of snow
over nrn MN associated with a weak shrtwv and upper level div with
the left exit of the 250-300 jet.
Tonight: Radar trends and shortwave range high res models suggest
that the area of snow will spread across Upper Michigan between 00z-
06z with some light accumulations of around an inch over the west
and smaller amounts where downslope low level sw flow prevails. 850
mb temps only to around -3C this evening will not favor any
significant lake enhancement. While most of pcpn should be snow, per
forecast wet-bulb zero heights, some rain may mix in near Lake
Superior.
Tuesday: although colder air will move into the region with 850 mb
temps dropping from -10C to -15C will only provide marginal
instability for wrly flow LES as inversion heights near 5k ft with a
dry 850-700 mb layer limit accumulation potential to another inch or
two. As winds veer to the wnw in the afternoon some light LES of an
inch or less is also expected east of Munising.
The main hazard will be the potential for higher winds over the
Keweenaw where momentum transfer fcst with decreasing stability
suggests winds will gust to around 45 mph, especially in favored
higher terrain west facing locations near KCMX. Because of the
combination of the high winds an light snow with some blsn, a
winter wx advisory was issued. Otherwise, conditions will remain
relatively mild with highs in the lower to mid 30s, warmest south
and east.
.LONG TERM...(Tuesday night through Monday)
Issued at 350 PM EST MON DEC 18 2017
The main forecast concerns for later this week into early next week
are the arrival of a low pressure system progged to track across the
Great Lakes region towards the end of the week, and then the arrival
of an bitterly cold arctic airmass early next week.
Tuesday night through Wednesday: As the surface pressure gradient
between the exiting low off to our east and an approaching area of
high pressure remains enhanced, strong and gusty winds will linger
Tuesday night into early Wednesday. With the wind direction
primarily out of the northwest, increased fetch and quasi-prolonged
stronger winds will allow large waves to build on Lake Superior
impacting the shoreline primarily east of Munising. Lake effect snow
showers will continue in the northwest wind snow belts Tuesday
night, but as the 850mb flow backs to the west-northwest throughout
the day, with warming temperatures and heights rise across the
region expect the lingering lake effect to impact the east and start
to diminish across the west.
Wednesday night through Friday: There is still quite a bit of spread
among the medium-range models in regards to the strength, track, and
timing of the the system expected to arrive later this week. Given
the longwave trough progged to dig south across the Dessert
Southwest, thinking the GFS/ECMWF are onto something with slowing
this wave down and broad, elongated southwest flow developing across
the central CONUS. This would favor the southern and northern
streams associated with this system to phase east of the region.
This idea is also further supported with the latest runs of the GFS
Ensembles and SREF. There certainly will be travel impacts across
the region as this system moves through, especially Thursday through
Friday; however, the exact locations of these impacts will depend on
where main frontogenesis band sets up. It is certainly too early
to pinpoint snowfall amounts and what locations will see the
highest accumulations. However, at this time given the track of
the surface and 850mb lows the impacts may be felt more west of
Lake Michigan and across the northern half of Upper Michigan where
lake enhanced snow looks possible. To reiterate, the more
significant impacts and accumulating snow will be highly depending
on the track and speed of the system. Those planning to travel
across the region should keep up to date on the forecast as the
details will become fine-tuned over the up and coming days,
especially after the main upper-level wave comes on shore.
Saturday into early next week: Although the models diverge with the
above mention system and overall impacts across Upper Michigan. As
the trough axis continue to slowly move east of the region, multiple
shortwaves are expected to rotate down across the region. This will
allow for multiple reinforcing shots of bitterly cold, arctic air.
It certainly looks like we will see the coldest temperatures of the
season by early next week. Lake effect snow will accompany this
colder air near Lake Superior, although with 850mb temperatures
progged to drop down to between -20 to -26C snow will be a bit less
efficient.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 530 PM EST MON DEC 18 2017
Conditions will fall back to MVFR/IFR tonight as light snow or lake
enhanced snow develops over the west. Westerly winds will favor
mainly MVFR conditions at KSAW. Will be gusty at KCMX late tonight
into Tue.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 416 PM EST MON DEC 18 2017
Southwesterly to 30 knots will veer wrly tonight with some gale
force gustst. As colder air moves in, winds will increase to gales
of 35 to 40 knots Tuesday and to around 45 knots over the east by
later Tuesdy afternoon into Tue night. With increasing wave heights
and colder air temperatures, freezing spray is possible Tuesday
night into Wednesday.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory until 1 AM EST Wednesday for MIZ001-003.
Lake Superior...
Gale Warning from 1 AM Tuesday to 4 AM EST Wednesday for
LSZ243>251-264>267.
Gale Warning from 10 AM EST /9 AM CST/ to 11 PM EST /10 PM CST/
Tuesday for LSZ162-241-242-263.
Lake Michigan...
None.
&&
$$
SHORT TERM...JLB
LONG TERM...Ritzman
AVIATION...07
MARINE...JLB