Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/20/17
Area Forecast Discussion
National Weather Service Bismarck ND
953 PM CST Tue Dec 19 2017
.UPDATE...
Issued at 941 PM CST Tue Dec 19 2017
No changes to the Winter Storm Warning and Winter Weather
Advisory for tonight through Wednesday night at this time. The
incoming 00 UTC global suite, and CAM suites through the 02 UTC
HRRR continue to wobble the axis of the heaviest snow between US
Highway 2 and Lake Sakakawea, around 6 to 8 inches storm total.
Given this continued variance, there is not enough confidence at
this time to adjust the areal coverage of the Winter Storm
Warning, and will continue to monitor observed trends through the
night for an early indication of where the band may be
establishing itself, supplemented by the 06 UTC global suite and
rapidly updating suites through the night. Adjustments to
headlines are certainly possible once confidence increases. One
thing that does seem certain is the likelihood for very little
snow during the day on Wednesday south of I-94.
UPDATE Issued at 545 PM CST Tue Dec 19 2017
Little change for the evening with this update. Will continue to
analyze the 18 UTC and incoming 00 UTC global suites, and rapidly
updating guidance for the evening should any modification to
ongoing winter headlines be necessary. The 18 UTC NAM/GFS were a
bit further south with the heaviest snowfall totals, although that
is not reflected as much in the CAM guidance at this time.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 152 PM CST Tue Dec 19 2017
Models now in general agreement in spreading snow across northern
North Dakota beginning late tonight and continuing through
Wednesday night. Consensus among the models suggests a widespread
3 to 5 inches north of Interstate 94 with a band of 6 to 8 inches
of snow northwest and north central, along the highway 2
corridor.
So placed the winter storm warning along the expected 6-8 inch
snow band with an advisory along the southern and eastern
periphery of the warning.
The snow will begin this evening across the southwest in a broad
warm advection field associated with the baroclinic zone initially
across Montana into western South Dakota.
By Wednesday, weak h850-700 mb frontogenesis is focused across
northwest into north central North Dakota with broad scale lift
above. The above mentioned ingredients, while not particularly
strong or outstanding for heavy snow, should be aided with a deep
layer dendritic growth zone seen on model soundings between
Williston and Minot. This tilts the decision in favor of more
efficient snow production there and went with a winter storm
warning for heavy snow.
As is common with snow, there will be a rather strong gradient
and the better accumulations will fall across portions of
northern Burleigh, northern Kidder and northern Stutsman with
southern sections of these counties getting on an inch or so.
Added mention of some patchy blowing snow Wednesday and Wednesday
night with the approaching pressure rise as the low tracks east.
However widespread blowing snow is not expected.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 152 PM CST Tue Dec 19 2017
The long anticipated change to much colder weather will be seen
this extended period as temperatures steadily decreases through
the period as a deep and cold upper low migrates southwest of
Hudson Bay. The primary concern will be the cold temperatures and
the associated bitter wind chills that arrive Christmas eve
through Christmas Day and beyond. The chances for snow will be
small due to the dry nature of the arctic airmass.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday night)
Issued at 941 PM CST Tue Dec 19 2017
Ceilings will lower into MVFR for most of the area through the
night. There is a chance of light snow south central and across
the James River Valley late tonight. Snow will increase across
northwest and north central North Dakota late tonight into
Wednesday morning. KISN/KMOT will see the greatest impacts on
Wednesday with LIFR/VLIFR conditions in snow expected through the
day. KJMS/KBIS will likely see their greatest impacts from snow
Wednesday afternoon and through the evening. KDIK will be on the
southern fringe of the snow band Wednesday, and will have to be
closely monitored as conditions may trend worse than what is shown
in the 00 UTC TAF.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM CST /2 AM MST/ Wednesday to 6
AM CST /5 AM MST/ Thursday for NDZ005-013-017>023-025-035>037.
Winter Storm Warning from 3 AM Wednesday to 6 AM CST Thursday
for NDZ001>004-009>012.
&&
$$
UPDATE...PA
SHORT TERM...WAA
LONG TERM...WAA
AVIATION...PA
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
828 PM CST Tue Dec 19 2017
.UPDATE... /DENSE FOG ADVY THRU 15Z/
After seeing most of the Hill Country fog up and a public caller
reporting of the fog being more dense than last night along Hwy 90,
have decided to move forward with the advisory. RUC Model soundings
already show a sharp but shallow inversion developed by 03Z, and this
should help sustain the decoupled winds for at least the evening
hours. Late tonight a few areas could mix out the inversion and
improve some vsbys.
&&
.PREV DISCUSSION... /ISSUED 759 PM CST Tue Dec 19 2017/
UPDATE... /FOG THIS EVENING/
Light westerly winds are decoupling early this evening which will
allow for more areas to experience overnight fog. Some patchy evening
fog is already forming over parts of the Hill Country and will
expand into the metro cities shortly. After midnight light drainage
winds are expected to disperse most of the fog above the escarpment
while shallow fog may continue to impact eastern portions of the
metro cities. Will monitor for another hour before deciding on a
possible Dense Fog Advy as the situation continues to evolve with the
clearing of skies and changes in wind.
Only other update change was to clear out the rain chances for the
SAT metro area.
PREV DISCUSSION... /ISSUED 547 PM CST Tue Dec 19 2017/
UPDATE...
00Z Aviation discussion below.
AVIATION...
A broken band of SHRAs and isolated TSTMs east of the diffuse cold
front and east of I-35 will continue east through the evening hours,
into East and Southeast Texas and away from the I-35 corridor TAF
sites. A mix of IFR and MVFR ceilings still persists at the I-35 TAF
sites. Improvement to VFR will take place 01Z-03Z. Very shallow
moisture trapped beneath developing inversion and de-coupling will
allow shallow fog layer to develop across southwestern areas late
this evening. The shallow fog layer may develop and advect eastward
overnight impacting SAT/SSF TAF sites. Appears northwest flow and
drier air toward AUS will limit the fog potential there. Have shown
LIFR visibility and ceiling at SSF and IFR visibility at SAT
developing 06Z, consistent with latest HRRR and LAMP guidance.
Conditions should improve to VFR at SAT/SSF after 15Z as inversion
breaks and mixing of dry air aloft with weak northwest flow develops.
AUS and DRT are forecast to remain VFR.
PREV DISCUSSION... /ISSUED 237 PM CST Tue Dec 19 2017/
SHORT TERM (Tonight through Wednesday Night)...
Cloud cover continues across the region this afternoon, but the fog
has dissipated for the most part with decent southerly flow in place
across most locations. The upper trough axis is now entering West
Texas with the main area of ascent now in North Texas moving to the
northeast. We still have enough weaker ascent for isolated to
scattered areas of light rain this afternoon. The best mid-level
forcing for our area is near the base of the trough axis in Val Verde
County and some scattered elevated echoes are showing up on radar in
response. Latest mesoanalysis shows no instability in this area and
not much is expected out of this. One should note that no model
guidance has picked up on this activity which could signal an
under representation to the upper lift actually occurring.
The latest surface analysis shows the associated Pacific front east
of Del Rio and this front is expected to push east through the
afternoon and evening hours. This boundary could serve as a focus for
surface development but would have to wait until it crosses the I-35
corridor before reaching better boundary layer instability where
current CAPE values are around 1000-1500 J/kg. It is currently 77 in
Gonzales with a dewpoint of 70 while San Antonio is 66 over 64.
Shear values would support organized convection, but with the main
upper forcing well to our north, am not anticipating a whole lot to
happen along the front this far south. Latest runs of the HRRR and
TTU WRF have been showing little in the way for deep convection. The
latest Day 1 outlook from SPC shows a marginal risk for our
northeastern counties and this seems reasonable given the strong
shear, but with lack of significant forcing and the front being
poorly defined, not expecting much more than a strong storm or two,
except if the forcing out west is being under represented.
Any precipitation is expected to move east of the area by the late
evening hours with the rest of the overnight period being dry. Some
of the high-res guidance is showing the return of fog to the southern
counties and will mention fog there from 06z through 15z tomorrow
morning. After any fog or low-clouds burn off, skies should finally
be mostly clear tomorrow with some passing high clouds which will
probably be a welcome change from this dreary weather we have had
the past few days. Highs will top out in the lower to middle 70s and
lows tomorrow night should be in the middle to upper 40s.
LONG TERM (Thursday through Tuesday)...
One more warm day is expected Thursday with highs back in the 70, but
skies will be turning cloudy once again as moisture advection returns
ahead of the next system. Within this moist advection regime, there
could be isolated showers across the Coastal Plains and will mention
a 20 PoP there. On Thursday night, the next upper trough axis will be
pushing into the central CONUS with a cold front pushing south
through the Plains. The GFS/ECMWF has slowed down the progression of
the cold front with the FROPA expected to occur during the day
Friday. Therefore lows and highs Friday are technically warmer than
the previous forecast but temperatures will drop into 40s and 50s
behind the front Friday night.
The next stronger push of colder air is still scheduled to occur
Sunday morning, but with southerly flow not expected to return
between the two systems, this front looks to be a dry front.
Temperatures behind it will be much colder with highs Sunday likely
in the 40s for most locations and highs Christmas remaining in the
40s. Looks like close to an area-wide freeze Christmas morning and
again on Tuesday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 50 75 51 74 60 / 20 0 0 - 30
Austin Bergstrom Intl Airport 49 74 47 74 63 / 30 0 0 - 30
New Braunfels Muni Airport 50 75 49 73 62 / 20 0 0 - 30
Burnet Muni Airport 46 71 48 74 55 / 10 0 0 - 30
Del Rio Intl Airport 45 75 47 75 54 / 0 0 0 0 10
Georgetown Muni Airport 49 72 48 75 58 / 20 0 0 - 30
Hondo Muni Airport 44 76 48 73 60 / - 0 0 0 20
San Marcos Muni Airport 49 75 49 75 62 / 30 0 0 10 30
La Grange - Fayette Regional 52 73 50 74 63 / 40 0 0 10 30
San Antonio Intl Airport 51 76 51 72 61 / 20 0 0 - 30
Stinson Muni Airport 51 75 50 74 62 / 20 0 0 - 30
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CST Wednesday for the following
counties: Atascosa...Bandera...Bastrop...Bexar...Blanco...Burnet...
Caldwell...Comal...De Witt...Dimmit...Fayette...Frio...Gillespie...
Gonzales...Guadalupe...Hays...Karnes...Kendall...Kerr...Lavaca...
Lee...Llano...Maverick...Medina...Travis...Uvalde...Williamson...
Wilson...Zavala.
&&
$$
Mesoscale/Aviation...Runyen
Synoptic/Grids...Oaks
Area Forecast Discussion
National Weather Service Wilmington NC
941 PM EST Tue Dec 19 2017
.SYNOPSIS...
Increasingly moist air ahead of an area of low pressure will
result in widespread rain and perhaps a brief rumble of thunder
Wednesday and Wednesday night. 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. Temperatures will dramatically cool in the wake of a
cold front Tuesday with Arctic air plunging across the Carolinas
by Wednesday of next week.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 945 PM Tuesday...Radar composites show rain has reached
the Upstate of South Carolina, falling from mid-level ceilings
of 7000 to 10000 feet AGL. The RAP has been the most reliable
among our operational models this evening showing this rapid
eastward expansion of precipitation. An earlier update this
evening raised PoPs after 1-2 AM, but I`m hesitant to raise
them farther as the rain will likely be encountering a drier
sub-cloud layer as it heads east. This was evident on the 00Z
CHS sounding which showed below-freezing dewpoints between
3000-10000 feet which will take some time to saturate Wednesday
morning.
I`ve tweaked overnight temperatures upward based on current
observations, and the likelihood that increasing cloudiness will
almost eliminate any substantial radiational cooling. Forecast
lows range from the lower to middle 50s -- only a little below
normal highs this time of year!
Discussion from 645 PM follows...
High pressure to the south will sink a little farther south and
east through tonight as a storm system tracks east from Texas
across the deep south toward Alabama by morning. At the same
time a cold front will drop slowly down from the north. The
associated shortwave aloft will move east riding around the mid
to upper ridge. This will enhance the lift out ahead of the
approaching low pressure system with moisture and clouds
streaming east into the Carolinas. Therefore expect increasing
clouds through tonight in a warm and moist air mass with low
temps between 50 and 55. As shallow cooler air makes its way
down from the north, deep warm and moist SW flow will overrun it
producing enhanced lift and increased clouds and pcp through
the day on Wed. The pcp will mainly be north of the area through
tonight but will include some pops across northern tier
counties as pcp spreads south by daybreak.
To the south of this band of pcp which is associated with greater
isentropic lift, expect showers and more convective type pcp in warm
sector ahead of the system mainly across South Carolina. Should see
more in the way of sunshine to the south and fewer showers to start
the day but as the day wears on, expect deeper richer moisture to
increase potential for shower activity to the south at the same time
rain spreads down from the north. Pcp water values around .65 inches
today will increase up to 1.3 inches by Wed morning and up to 1.5
inches by Wed aftn, in increasing W to SW flow ahead of the system.
Low level flow will increase up to 45 to 50 kt out ahead of trailing
cold front mainly across SC. Dewpoint temps will reach up near 58
late Wed aftn but sounding profiles lack instability and therefore
expect some heavier rain showers with some gusty winds possible late
Wed aftn into early evening mainly nosing into northeast South
Carolina. May see an isolated thunderstorm but expect any storms
mainly west and south of local forecast area.
Cooler air will make its way down from the north with sfc temps near
60 Wed aftn dropping behind it, mainly over NC zones while temps in
the warm sector over SC will reach near 70.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 300 PM Tuesday...Rain to be shutting off from N to S as cool
wedge pushes in as well as from W to E as lift associated with
shortwave moves offshore. Depending on rainfall rates some areas may
net another tenth of an inch before the measurable rain ceases.
Thursday appears to remain rather cloudy. The cool low level air
will continue to undercut the layers above leading to gentle ascent.
This will be bolstered as the flow above the boundary layer backs to
SW or SSW increasing the upglide occurring atop the surface-based
layer. Surface troughiness is forecast to develop off the coast
Thursday night despite a lack of any features aloft. This feature
may be related to surface baroclinicity along the west wall of the
Gulf Stream. It also seems to have little impact on local weather
save for perhaps winds over our marine environment.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 300 PM Tuesday...A series of strong shortwaves will help
to deepen an upper trough across middle America this weekend.
This trough will finally progress to the east coast for Christmas
and then offshore by Tue, replacing a strong, moist and deep SW
flow with a W and NW flow. At the surface, a wedge of high
pressure will be in place across the Carolinas with a coastal
trough positioned just offshore at the start of the period. The
wedge will break down on Fri with the strong ridge of high
pressure moving offshore Fri night. The coastal trough is
expected to dissipate Fri eve. Strong low pressure will move
rapidly NE across the Ohio Valley Fri night and into eastern
Canada Sat with a trailing cold front struggling to move east of
the Appalachians. This front should finally push off shore
during Mon. An Arctic airmass will build in from the W Tue-Wed.
The forecast period will be largely unsettled, book ended by
dry days Fri and Tue. At this time, scattered showers are in the
forecast for the weekend and on Christmas day. The biggest headline
will be the unseasonable warmth and some locations may be near
record highs Sat and Sun with developing S and SW winds. This
record warmth may result in low stratus and fog/sea fog. Clouds
are expected to dominate after Fri with Christmas Eve and
Christmas day being perhaps the cloudiest.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 00Z...Another rather low confidence situation with respect to
ceilings and the timing of the onset of precip. Think the models may
be too quick to introduce IFR conditions, as the warm front hangs
north of the region at daybreak. Look for deteriorating conditions
from north to south as a wedge starts to set up in the afternoon.
All terminals should be solidly in IFR conditions by 20-22z, with a
moderate northeast wind.
Extended Outlook...MVFR/IFR/showers through Thur morning,
and then again Thurs night. VFR Fri. VFR/Possible showers Sat/Sun.
&&
.MARINE...
NEAR TERM /THROUGH WEDNESDAY/...
As of 945 PM Tuesday...Southwesterly winds should veer more
westerly with time overnight. Observations at 9 PM were in-line
with our going forecast and no changes are necessary. Discussion
from 300 PM follows...
Quiet marine conditions will continue for most of the period.
Southwesterly winds this afternoon will veer back to the west by
Wed morning remaining less than 15 kt. Seas will basically
remain less than 3 ft through tonight. A storm system will
approach from the west on Wed as a cold front drops down from
the north. Winds will increase out of the southwest through Wed
aftn as the system approaches and could push seas up to 3 to 5
ft over southern waters off the coast of northeast SC by late
aftn, while winds should remain light and more variable along
the cold front as it drops south, with winds behind it picking
up out of the north toward the evening. Overall, expect to
squeak by without any precautionary headlines, but will have
increasing winds and seas by Wed eve, as well as an increase in
rain or shower activity.
SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 300 PM Tuesday...Rather unsettled weather expected for the
first half of the period. Frontal boundary will be sinking southward
as cold surge of high pressure pushes into the Carolinas. The
resulting NE flow could push conditions close to SCEC/Advisory
thresholds mainly over NC waters where the high will be strongest.
Short period, confused seas farther south from the abrupt turning and
increase in winds could still make for less than spectacular
navigation conditions even if short of criteria. The NE flow will
remain in place through the period as not only the high shows little
movement but weak low pressure also develops off the coast.
LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 300 PM Tuesday...A wedge of high pressure will be in place
across the Carolinas with a coastal trough positioned just
offshore. The wedge will break down on Fri with the strong ridge
of high pressure moving offshore Fri night. The coastal trough
is expected to dissipate Fri eve. Strong low pressure will move
rapidly NE across the Ohio Valley Fri night and into eastern
Canada Sat with a trailing cold front struggling to move east of
the Appalachians. This front should be situated very near the
waters late in the period and on Mon. NE winds Fri will veer to
SE late Fri and to S Fri night. SSW to SW winds will dominate
through the weekend. The strongest winds this period will be
during the weekend, but no higher than 15 kt. Seas of 2 ft Fri
and 2 to 3 ft Fri night will build to 3 to 4 ft Sat and 4 to 5
ft by Sat night. Seas should then trim to 3 to 4 ft during Sun.
The weather will be unsettled with scattered showers expected
for much of the period. In addition, abnormally warm and
sufficiently moist air will coincide with a favorable wind
direction this weekend, producing an environment that will be
conducive for sea fog development.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.
&&
$$
SYNOPSIS...
NEAR TERM...TRA/RGZ
SHORT TERM...MBB
LONG TERM...RJD
AVIATION...MRR
MARINE...
Area Forecast Discussion
National Weather Service Jacksonville FL
856 PM EST Tue Dec 19 2017
...WIDESPREAD DENSE FOG EXPECTED THROUGH EARLY WEDNESDAY
MORNING...
.UPDATE...
Good setup for advection and radiation fog tonight with JAX 00z
sounding showing moist low levels and substantial dry layer above
that. Weak sfc high pressure ridge is over FL and into parts of
GA with light to calm winds tonight. Mid level ridge is noted
across the southeast U.S.
Based on current obs have initiated the first part of dense fog
advisory extending through parts of southeast GA and northeast FL.
This is where HRRR and SREF have good consensus of dense fog. A
few sites have reported 1/4 and 1/2 mile so far over the wrn zones
and with light southwest flow the low cigs and fog will spread
east and northeast while temps cool through the 60s. Have bumped
up temps slightly based on cool bias from last night. The advisory
goes through 15z but believe the dense fog may lift a little
sooner...especially over parts of southeast GA as southwest winds
increase in the morning hours to about 5-10 mph.
&&
.AVIATION...Have gone a little more pessimistic on the TAFs
tonight and may lower even further based on sfc observations
coming from the Suwannee Valley and parts of southeast GA.
Indicated VLIFR to LIFR with latest TAFs after 08Z-10z time frame.
Low vsby and cigs will continue through about 14z-15z time frame
and improve through late morning. VFR should be developing from
16z-18z. Sct-bkn cumulus expected most areas in the aftn with
some cigs flirting with MVFR (around 2500-3000 ft) at times.
&&
.MARINE...Sea fog will impact portions of the nearshore waters
tonight...restrictions down to a mile or less over some parts of
the waters. Cannot rule out a marine dense fog advisory for parts
of area waters late tonight and early Wednesday morning. Light
and variable winds in the evening will become south to southwest
and increase to near 10 kt. Seas of about 2 ft or less. High
pressure will shift to the south southwest 15-20 knots on
Wednesday ahead of a cold front.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 60 77 59 72 / 0 30 40 10
SSI 60 75 61 69 / 0 10 20 10
JAX 60 80 61 75 / 0 10 30 10
SGJ 61 79 61 75 / 0 0 30 10
GNV 59 79 61 79 / 0 10 40 20
OCF 59 80 61 80 / 0 0 30 30
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Dense Fog Advisory from midnight tonight to 10 AM EST Wednesday
for Alachua-Baker-Bradford-Union.
Dense Fog Advisory until 10 AM EST Wednesday for Columbia-
Gilchrist-Hamilton-Suwannee.
GA...Dense Fog Advisory from midnight tonight to 10 AM EST Wednesday
for Appling-Brantley-Charlton-Pierce-Wayne.
Dense Fog Advisory until 10 AM EST Wednesday for Atkinson-Bacon-
Clinch-Coffee-Echols-Jeff Davis-Ware.
AM...None.
&&
$$
Shashy/Nelson/McGinnis
Area Forecast Discussion
National Weather Service Marquette MI
535 PM EST Tue Dec 19 2017
.SHORT TERM...(This evening through Wednesday)
Issued at 414 PM EST TUE DEC 19 2017
Water vapor imagery and RAP analysis show a trof over the Upper
Great Lakes. Colder air is surging into the area on gusty wnw winds
in the wake of shortwave and cold fropa earlier today. With steep
mid level lapse rates associated with shortwave, a few lightning
strikes were noted on the lightning detection network n of the Soo
early this aftn. Increasingly colder air has been supporting an
increase in les this aftn. However, strong low-level winds are
displacing these shsn mostly passed the Keweenaw and farther inland
over western Upper MI into Baraga and Marquette Counties. Winds over
the Keweenaw have been gusting at or above wind advy criteria of
45mph, but very little snow has fallen there, so there have been no
issues with snow/blsn there.
As winds diminish over the w this evening, expect les coverage to
increase over the Keweenaw. However, inversions will also fall to 4-
5kft, keeping the les in check. DGZ will solidly fill most of the
convective layer, so snow will fluff up with increasing snow to
water ratios. That said, not expecting much in the way of snow
accumulations...only an inch or two for most locations. Although
winds may gust to around 45mph for another few hrs, winter wx advy
does not appear warranted for these conditions. To the e, longer
fetch and more persistent low-level convergence will support greater
snow accumulations in the 1-4 inch range, maybe locally 5. Gusty
winds, diminishing overnight, will also lead to blsn in open areas.
Will maintain advy for Alger/Luce and extend thru the nighttime hrs.
Inversions hold fairly steady thru the day on Wed with the DGZ still
filling most of the convective layer. As a result, where nw winds
are off Lake Superior, expect sct/nmrs shsn to continue with a
fluffy inch or two of accumulation, perhaps locally up to 3 e. Winds
will steadily diminish thru the day as high pres ridge noses into
the Upper Lakes. Snow spreading out across the Northern Plains in
developing waa/isentropic ascent regime will stay w of Upper MI thru
the aftn.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 353 PM EST TUE DEC 19 2017
Potential for light to moderate snow Wednesday night into Thursday
with another system skirting to the southeast of the U.P. Friday
night into Saturday and the coldest air of the season expected this
weekend into early next week
Wednesday night through Saturday: Low pressure is progged to slide
from the Central Plains Wednesday night, across the mid-Mississippi
Valley Thursday and Thursday night and into the eastern Lakes Friday
into Friday night. Wednesday night into Thursday at surface trough
is progged to set up across the CWA as shown by analyzing the 850mb
Theta-E gradient along with modeled 850mb/surface winds. The
combination of the aformentioned features, along with deeper
moisture/forcing pushing into the area, will allow for some light to
moderate snow across much of the U.P. through Thursday evening.
Looks like most of the area would see around 3 to 6 inches through
Thursday evening. As the low strengthens/redevelops across southern
Lower Michigan late Friday night into Saturday, widespread snow is
expected to slide across much of eastern and southeastern WI into
northern Lower Michigan. Some deeper moisture may end up brushing
the far southeastern half of the U.P. along with some forcing on the
fringes of the low pressure system, depending how far east the low
track ends up. This may give an additional 1 to 3 inches over the
far southeastern portion of the U.P., mainly near Lake Michigan. The
GFS is the most aggressive with this scenario, deepening the low to
around 990-986mb Saturday morning and is a bit farther west (which
would give several inches of snow). This appears to be the outlier
as the Canadian/NAM/EC all have the low much weaker/slower and
farther east, giving little to no impact to any or a very small
portion of the U.P. Friday night into Saturday. 850mb temperatures
are not expected to be much colder than
-8C, so any lake enhancement will be very marginal at best. The
potential still exists for some heavier snow over the southeastern
portions of the U.P.; therefore, those with travel plans to the
south and east of the U.P. Friday into Saturday will need to stay
tuned for updates.
Saturday night through the rest of the extended: Much deeper
troughing is progged to slide across much of the eastern half of the
CONUS, allowing for some of the coldest air of the season to slide
into the CWA. This will be especially true Sunday through the middle
of the upcoming work week. In fact, models are showing a lobe of
Arctic air sliding into the Upper Peninsula through this time period
with 850mb temperatures progged to drop as low as -30C. This would
give high temperatures around zero or in the single digits above
zero through this time period. Overnight lows will likely run in the
mid to upper teens below zero over the west half, while the east
half will likely see sigle digits below zero to low teens below zero
for this time period. While winds will likely be fairly light during
this time period, it won`t take much for wind chills to drop into
the 20 degree range or lower below zero. Temperatures aloft will, of
course, be plenty cold enough for lake effect snow, mainly for west
to northwest wind snow belts. At this point, not expecting any major
system during this time period and it will likely be too cold to get
larger (accumulating snowflakes); however, any lake effect snow that
does occur during this time period will be very effective at
reducing visibility due to the larger number of very small flakes.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 535 PM EST TUE DEC 19 2017
MVFR cigs should prevail at KIWD/KCMX thru the fcst period. At KSAW,
VFR conditions should prevail, but some lowering of cigs to MVFR may
occur Wed morning. Developing lake effect shsn will affect mainly
KIWD/KCMX, resulting in some vis fluctuation from falling snow and
blsn. Not out of the question that some brief IFR vis could occur at
KCMX this evening.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EST TUE DEC 19 2017
Ongoing gales on Lake Superior will diminish to blo gale force from
w to e tonight as pres gradient slackens with approach of sfc high
pres ridge from the w. The strong winds/high waves and colder air
will lead to freezing spray as well. Winds will continue to diminish
Wed into Wed evening as high pres ridge arrives. Winds will increase
on Thu, mainly over western Lake Superior, but gales are not
expected. Another period of stronger winds will occur over the
weekend as an arctic air mass moves into the area. Could be some
gales with freezing spray returning.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory until 7 AM EST Wednesday for MIZ006-007.
Lake Superior...
Gale Warning until 4 AM EST Wednesday for LSZ243>251-264>267.
Gale Warning until 11 PM EST /10 PM CST/ this evening for LSZ162-
241-242-263.
Lake Michigan...
None.
&&
$$
SHORT TERM...Rolfson
LONG TERM...KEC
AVIATION...07
MARINE...Rolfson
Area Forecast Discussion
National Weather Service Raleigh NC
944 PM EST Tue Dec 19 2017
.SYNOPSIS...
A cold front will drop southward through North Carolina tonight,
before stalling near the North Carolina and South Carolina border
toward daybreak. Low pressure will track eastward along this front,
crossing South Carolina Wednesday. High pressure will extend into
the region from the north Thursday into Friday.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 944 PM Tuesday...
Timing of rain developing late tonight/early Wednesday is the main
issue this evening.
Cloudiness continued to increase and thicken over NC this evening
with the approach of the mid/upper level short wave trough from the
ARKLATEX region. Rain was spreading eastward along a developing warm
front extending from NE Texas into central AL. As a surface wave
develops along the boundary and tracks eastward, WAA rains will
spread eastward across the Tennessee Valley region and Appalachians
of western NC overnight. The warm front is expected to set up just
south of the NC/SC border. With a residual dry boundary layer over
much of western and northern NC, characterized by dew points in the
30s/40s, much of the initial 2-3 hours of rain will go into
saturating the boundary layer and not reaching the ground. Dew
points in the 50s/60s observed over GA and portions of SC will
remain hung up south of the warm front, along the NC/SC border area
where the wave of low pressure is forecast to track Wednesday. For
the overnight, expect thickening and lowering overcast. A chance of
rain after 400 am in the SW Piedmont. Lows in the 40s NE and 50s SW.
The latest HRRR indicated that the western and southern sections
would see the measurable rain develop between 500 and 800 AM. The
rain is expected to spread eastward into the Greensboro,
Fayetteville, and Raleigh areas between 600 and 800 AM, reaching the
I-95 corridor around Rocky Mount by mid-morning. Temperatures should
be warmer early, then fall during the day as the rain falls and
evaporatively cools the air. As the wave tracks along the boundary
to our south, surface winds will become NE then N during the
afternoon keeping the temperatures falling through the 50s south and
40s north.
&&
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 220 PM Tuesday...
A raw and rainy day expected. The low level frontal zone will remain
situated roughly along the NC/SC border as low pressure tracks
eastward along it. Strong and deep lift will be generated by intense
low level mass convergence (including a 40-50 kt 850 mb swrly jet
slamming into the frontal zone) and moisture transport, along with
vigorous upper divergence and decent mid level DPVA. There is little
doubt that everyone will see measurable precip (and some will see
quite a bit), so have gone with categorical pops everywhere Wed.
With projections of such strong/deep ascent and PW well over 200% of
normal, periods of heavy soaking rain are likely. Storm total
rainfall should range from 0.7 N to nearly 1.5" over the SW CWA, and
local totals over 2" are possible. This could result in some urban
and street flooding, especially in poor drainage areas (exacerbated
by leaf-clogged drains). The surface low, lift mechanisms, and deep
moisture will all be exiting off the Carolina coast Wed evening, so
will taper pops down and out from WNW to ESE shortly after midnight,
although a batch of trailing mid level moisture back across NC will
result in just partial clearing late as surface high pressure builds
in from the north. Clouds/rain will hold temps down, with highs just
49-57, about a category above tonight`s lows. Cooler air will pour
in from the north Wed night, resulting in lows of 33-40. -GIH
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 145 PM Tuesday...
Thursday and Friday: A largely dry forecast with moderating
temperatures. The subtropical ridge will build northward into the
region through Friday as a strong low pressure/frontal system
approaches from the west. Flow aloft over Central NC will be
increasingly southwesterly with time, increasing mid to upper level
moisture and thus cloud cover. At the surface, a CAD wedge will be
in place through at least Friday afternoon, with north-northeasterly
flow on Thursday becoming more easterly then southeasterly as the
high retreats and the wedge airmass begins to erode. With the above
in mind, Thursday is expected to be the coolest day, with highs
topping out in the upper 40s to low 50s, despite relatively clear to
partly cloudy skies and dry weather. The weather pattern will begin
to change Friday night as the wedge erodes and southerly flow
increases. Expect chances for rain to increase across the west
Friday afternoon into Friday night.
Saturday through Tuesday: A cold front associated with a deepening
system moving through the eastern Great Lakes will approach the area
Saturday. Very mild air ahead of the front will send temperatures
soaring into the 60s and lower 70s Saturday before showers move into
the area in the afternoon. The front will become stationary along
or just east of the Appalachians Saturday night until at least
Sunday night, progressing through the area by Monday. Will continue
to carry chance of rain over Central NC through Monday. High
confidence at this time that the front and it`s associated rainfall
will exit the region on by Monday late afternoon/evening, with much
drier and colder air advecting in behind it. High pressure and
associated cold airmass will build into the area from the lower
Mississippi Valley on Tuesday.
&&
.AVIATION /18Z Tuesday through Sunday/...
As of 125 PM Tuesday...
The fog from earlier this morning has dispersed, leaving VFR
conditions across central NC. VFR conditions will persist through
this evening and into the overnight hours, albeit with an increase
in mid clouds (based above 10,000 ft AGL) from the west as a surface
low and upper disturbance approach. Cigs will steadily lower through
the night, finally dropping to MVFR shortly after 08z at INT/GSO,
10z at RDU/FAY, and 12z at RWI as widespread rain overtakes the area
from the west. IFR conditions are likely at all locations toward the
end of the TAF valid period (after 15z). Light surface winds from
the SW will veer around to NE by Wed morning.
Looking beyond 18z Wed: Poor aviation conditions will dominate at
all sites through Wed night, although there may be some brief
improvement to VFR overnight. VFR conditions are expected Thu,
followed by a trend to MVFR or IFR Thu night into Fri morning as low
level moisture returns. The chance for rain and sub-VFR conditions
returns Sat, lasting through Sun, as a front moves in from the west
and stalls over the region. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Hartfield
NEAR TERM...Badgett
SHORT TERM...Hartfield
LONG TERM...KC/Franklin
AVIATION...Hartfield
Area Forecast Discussion
National Weather Service Shreveport LA
542 PM CST Tue Dec 19 2017
.AVIATION...
Showers with embedded thunderstorms along with LIFR ceilings and
visibilies expected across area terminals overnight. Precipitation
to diminish by 20/15Z with MVFR ceilings and visibilities
continuing through 20/18Z. Conditions to improve to VFR after
20/18Z. Otherwise, south winds around 5 to 10 knots tonight to
become west on Wednesday. /05/
&&
.PREV DISCUSSION... /issued 424 PM CST Tue Dec 19 2017/
DISCUSSION...
A large area of strong isentropic ascent has spread over the
ArkLaTex region today ahead of a potent upper trough moving east
through the Texas Panhandle and north of a warm front that was
located just north of Interstate 20. Latest mesoanalysis indicates
a tight theta-e gradient along the warm front, and most of the
rain is occurring just north of this gradient. This trend should
persist through the night. There is pretty good agreement among
most of the models so far, and the HRRR has been handling this
system well. Therefore, it is expected that the warm front will
not move too much farther north, perhaps to the Arkansas/Louisiana
border, so I have kept the highest QPF amounts along and just
north of this position. Meanwhile, a surface low, with a weak cold
front trailing south, should develop this evening in North Texas
ahead of the approaching trough. As the entire system begins to
lift east and northeast this evening, an increase in convective
coverage and intensity is expected both along the warm front and
the cold front from Central Texas northeast into Central Arkansas.
The highest QPF amounts should be in Southern Arkansas where
another two to three inches of rain are possible. A couple of
severe thunderstorms cannot be ruled out tonight, but the overall
risk is low. Damaging winds and hail will be the primary threats.
A few showers will linger into Wednesday morning on the west side
of the departing trough, mainly east of a line from Hochatown OK
to Jena LA, but all precip will exit the area by noon.
Temperatures should warm nicely into the 70s in most locations
Wednesday and Thursday.
A long-wave upper trough over Hudson Bay and a strong upper ridge
extending north along the West Coast of the U.S. and into the
Arctic Ocean, will open the way for Arctic air to affect much of
the country during the extended periods of this forecast. The
first cold front is still expected to arrive Friday. Model
guidance is showing considerably better agreement and run-to-run
consistency today compared to previous days. A shortwave trough
rounding the base of the long-wave trough will help drive the
first front through the area. Showers and thunderstorms will once
again develop along this front. While the models are in good
agreement with the synoptic evolution, significant timing
differences still exist. The GFS is more progressive than the
ECMWF and clears all rain out of the area by Saturday morning. The
ECMWF is about 6 hours slower. I began to trend rain chances back
slightly early Saturday morning, but maintained chance PoPs
through the daytime Saturday to account for the slower ECMWF and
to maintain consistency with previous forecast packages.
The bulk of the Arctic air will begin to arrive Saturday night and
into Sunday as a secondary cold front dives southward. The medium
range models continue to suggest some precip will develop and move
south across Kansas, Oklahoma, and Arkansas as the longwave
trough axis moves across the Central CONUS. However, the models
are also dissipating this precip just as it reaches Southeast
Oklahoma and Southern Arkansas late Sunday night/Monday morning.
Therefore, I have kept the forecast dry beyond Saturday evening.
No wintry precipitation is currently anticipated during the next 7
days.
An extended period of cold weather is expected heading into early
next week as the cold Arctic high pressure moves overhead.
Overnight low temperatures Sunday night and Monday night will
likely fall into the low to mid 20s areawide while daytime highs
struggle to warm into the mid to upper 40s.
CN
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 57 70 49 74 / 90 10 0 10
MLU 61 73 48 73 / 80 20 0 10
DEQ 52 66 45 71 / 100 20 0 0
TXK 55 67 49 72 / 100 10 0 0
ELD 56 67 46 72 / 100 20 0 10
TYR 54 69 49 74 / 90 0 0 10
GGG 54 70 48 74 / 90 10 0 10
LFK 56 72 49 73 / 70 0 0 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
05/09