Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/21/16
Area Forecast Discussion
National Weather Service Binghamton NY
944 PM EST Tue Dec 20 2016
A low moving through southern Canada will bring a few clouds and
perhap a few snow flurries to the Tug Hill of New York, otherwise
conditions will be dry and seasonable into Thursday.
.NEAR TERM /THROUGH WEDNESDAY/...
Updated at 9:30 PM... No significant changes to the current
forecast. Surface low tracking east across central Ontario and
Quebec with a weak surface trough extending to the south over NY
and Pa. Just some high clouds over NY and Pa associated with this
feature through this evening. Some lower clouds can be seen
sagging southeast across southern Ontario and northern Lake
Ontario and these may show up over the northern half of NY toward
morning along with a few light flurries. Previous discussion is
Few clds along a sfc trof aprchg from the west sliding into the
area this aftn. HRRR and NAM show the psblty of a few lgt snow
shwrs over xtrm nrn Oneida cnty late tngt and into early Wed as
the flow becomes more wly along the lake and upr wv comes thru
with the core of the cold air. Otrw...just a few clds with the
system as it passes. Waa begins almost before dawn Wed and any le
will end quickly by mid mrng. Balance of Wed looks dry with incrsg
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
2 pm update...
Warmer weather continues but only slightly above normal. For this
period most of the precipitation will be snow. Qpf is light so
snow accumulations also light and mostly at higher elevations in
the far north of the cwa.
This system will track east to our north. The surface low moves
through the upper Great Lakes into southeast Ontario Wednesday
night. Aloft is a broad upper level trough and short wave. Not
very deep and it is transitory. Warm frontal snow late Wednesday
night. A cold front moves through Thursday morning mostly dry
followed by a secondary cold front late Thursday. 850mb temps at
-8c will help a little to add moisture. A 290 flow will keep most
of the snow across the usual lake effect areas in central
NY...eastern Finger Lakes to Mohawk Valley and northern
Susquehanna Region. Afternoon temperatures in the mid and upper
30s could cause a mix of rain and snow showers. High pressure
builds in from the southwest late Thursday night to stop any
lingering snow showers. Lows again in the 20s.
Friday the high is in control at the surface with more dry air.
Aloft a weak ridge builds in. Highs again in the 30s.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
2 pm update...
Friday night to Sunday a zonal flow aloft with mild air. A weak
front will bring some sprinkles and flurries mostly Saturday
afternoon and evening. Afternoon high 35 to 40 so roads should be
able to remain only wet.
Sunday a break with another dry Canadian high pressure. Models
agreeing better on the next system. This is a large low and deep
upper level trough. The track is to the west and north so most of
this will be rain with temps in the 40s. Rain comes in Monday
ahead of the cold front. Monday night rain changes back to snow or
a mix but really cold air will stay to the north. Tuesday back in
the 30s with showers across NY.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Some high clouds will drift across the area tonight with VFR
conditions. Patchy MVFR cigs could develop at RME Wednesday
morning otherwise VFR conditions will continue through the day
Wednesday with scattered clouds.
Winds will be mostly from the southwest at 5 to 10 kts tonight
shifting to west at 5 to 10 kts Wednesday.
Wednesday night...Mainly VFR.
Thursday through Thursday Night...Restrictions possible due to
snow or wintry mix, esp over NY stations.
Saturday...mvfr/ifr rain and snow shwrs
Area Forecast Discussion...Updated
National Weather Service Billings MT
738 PM MST Tue Dec 20 2016
Minor update to add slight chance pops for some isolated light
showers crossing central zones this evening. Line of light shower
activity moving southeast along a Roundup to Reed Point line at
730 pm is associated with the front edge of strong mid level
subsidence. Radar showing 50 to 65kts of wind in this area heading
southeast toward Billings area, and latest RUC and HRRR
corroborate this idea. Expect gusts of 40 to 55 mph along this
line as it continues to progress southeast over the next few
hours. Strongest winds will be in the higher hills with less winds
down into the valleys. Gusty winds should last an hour or two
behind the wave, calming down overnight. Rest of forecast in good
.SHORT TERM...valid for Wed and Thu...
Water vapor imagery shows flat ridging over MT/WY with an upstream
Pacific shortwave over WA/BC moving toward the northern Rockies,
with 120 kt H3 winds per the latest mesoanalysis. 1-2mb pressure
falls noted at 20z over north central MT, so although the
pressures over eastern ID and YNP have been decreasing, the
overall strength of the lee side trof has increased over the past
few hours. Livingston and Nye have already seen 60+ mph gusts
earlier today, and they should again in the pre-frontal
environment over the next couple hours. Then post-frontal winds
Cold front and synoptic subsidence arrive early this evening. This
and favorably oriented gradient will allow for strong west winds
to develop across our western foothills including Big Timber and
Harlowton, with gusts likely to approach 65 mph per the mid level
winds. Will make no changes to any of our wind highlights
currently in effect thru tonight. Windy conditions will overspread
the lower elevations this evening with 850mb winds to 50+ kts.
Near surface lapse rates should remain more stable away from the
foothills, given the influence of our snow cover and peak winds
during the nighttime hours, so do not feel there is a high wind
risk further east. Nonetheless that`s a lot of wind with synoptic
downward motion, so have raised wind gusts a bit more and have
issued a wx story regarding the overall windy conditions
anticipated across the lower elevations tonight. Look for 30-45
mph gusts with near 50 mph on the ridges.
Winds will begin to decrease by Wednesday morning as surface and
mid level trofs shift east allowing for a return of upper level
ridging. Downslope gradients will remain in place along the
foothills, and it certainly will be windy with WNW winds
persisting thru the day in our east.
Conditions become more favorable for gap flow again Wednesday
night and Thursday, but w/o as much support from the mid level
flow which will be significantly weaker than today. Due to the
gradient and low level stability will keep enhanced SW winds in
place thru Thursday, and have extended wx story for Livingston to
include these periods, but not sure if an additional advisory will
As for weather other than wind: Snow showers currently affecting
our western mountains and this will continue into this evening. A
few light rain/snow showers possible in our east away from the
stronger downslope influence over the next several hours, until
shortwave moves through. A dry period of wx is then in store late
tonight through Thursday per the aforementioned ridging. Onset of
moister Pacific flow will introduce potential for pcpn over our
western mountains by late Thursday night.
.LONG TERM...valid for Fri...Sat...Sun...Mon...Tue...
Upper ridging and low-level downsloping should keep much of the
lower elevations dry Friday-Friday night. ECMWF brings some
moisture into the mountains in southwest flow, so have some snow
showers there. Next round of snow looks to move into south
central MT Saturday afternoon/evening...extending eastward to the
rest of southern MT and north central WY Saturday night. Snow
could well continue into Sunday...tapering off for south central
MT Sunday night and for southeast MT Monday morning. Model
differences exist for this system, though, with the ECMWF and its
ensemble mean more organized, slower, and taking a more western
track, and the GFS more disorganized with its stronger low taking
a more eastern track, farther away from our area. At this time
leaning more towards the ECMWF solution. It is too early to pin
down precise timing and snowfall amounts, but potential is there
for accumulating snow and impacts Saturday night-Sunday night.
On Monday, region is under northwest flow, so think that scattered
snow showers are possible over the region. Depending on the speed
and track of the weekend system, southeast MT could still have steady
snow for part of the day Monday. Next Tuesday, shortwave ridging
looks to give way to some troughiness, which could generate a few
snow showers west of Billings and in the southwestern mountain
Temperatures should be slightly above normal on Friday, then drop
a bit below normal for Saturday and remain cold through Monday.
Some moderating for Tuesday with highs getting closer to seasonal
A Pacific cold front will move through the region bringing
increased W winds across the forecast area beginning late this
afternoon and lasting through the night. Expect gusts of 45-55
kts at KLVM, Big Timber and 3HT, and 30-45 kts further east
including KBIL, KSHR, KMLS and KBHK. Otherwise, VFR will prevail
across the lower elevations with some light rain and snow showers,
mainly this evening. The Beartooth/Absaroka and Crazy Mountains
will be obscured in snow showers. Dry conditions with VFR flight
conditions can be expected across the area late tonight through
.PRELIMINARY POINT TEMP/POPS...
Wed Thu Fri Sat Sun Mon Tue
BIL 029/035 018/035 022/039 019/025 010/015 003/018 014/030
20/N 00/N 11/B 13/S 55/S 32/J 11/B
LVM 026/035 017/033 023/039 021/034 010/018 005/021 016/035
30/N 00/N 13/W 45/S 54/S 32/J 12/J
HDN 027/036 009/033 017/035 014/022 012/016 901/016 008/029
20/N 00/B 01/B 02/S 55/S 32/J 11/B
MLS 028/036 013/034 017/033 012/024 009/014 902/013 003/028
30/Q 00/U 01/B 12/S 55/S 33/S 11/B
4BQ 027/035 010/035 015/036 014/030 012/018 901/017 008/031
30/Q 00/U 01/B 11/E 45/S 33/S 11/B
BHK 027/035 013/034 015/034 011/024 010/015 901/015 002/027
31/Q 00/U 01/B 11/E 46/S 33/S 11/B
SHR 023/035 007/035 015/038 014/034 012/018 001/018 008/036
10/N 00/U 01/B 01/B 55/S 32/J 11/B
MT...High Wind Warning in effect until 8 AM MST Wednesday FOR
Wind Advisory in effect until noon MST Wednesday FOR ZONES
Area Forecast Discussion
National Weather Service Hastings NE
459 PM CST Tue Dec 20 2016
.SHORT TERM...(This evening through Wednesday)
Issued at 343 PM CST Tue Dec 20 2016
The SREF has been hinting at the possibility of fog late tonight
into Wednesday morning across our southeastern zones, primarily
over north central Kansas. The HRRR thus far has not been showing
similar signs. Have decided to add patchy fog to our southeastern
most counties for late tonight, but confidence is rather low.
A cold front will swing through during the day on Wednesday, but
with good mixing and the upper system staying well north it will
only be a glancing shot of cooler air. Therefore, highs on
Wednesday should still be in the mid 40s.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 343 PM CST Tue Dec 20 2016
Overview...Temperatures should be around or above normal through
Christmas day. The primary concern will center around a strong
upper low that will track across the northern/central plains on
Christmas. We should then turn colder just after Christmas behind
the departing storm system. Given the current forecast track of
the upper low, it appears thunderstorms and possibly even severe
thunderstorms will be our primary hazard with this system on
Christmas, with most of the snow currently expected to be over the
Christmas Eve into Christmas Day:
The 12Z GFS/ECMWF/GEM and a vast majority of ensembles are all
indicating above freezing 850mb air for Christmas Eve through
Christmas Day. I see very little if any chance of frozen
precipitation Christmas Eve or through at least sunset Christmas
Day given the predominate storm track in these major models.
Therefore, I raised Saturday night/Christmas Eve min temperatures
to above freezing and will go with rain during this period.
I also increased the chance for thunderstorms on Christmas day
for all areas. The 12Z ECMWF is the slowest model and would give
us the best chance for thunderstorms. The main question with
thunderstorms will be the timing of the cold frontal passage on
Christmas Day and if the storms will form over our forecast area
or off to our east. Timing is still rather uncertain given it is a
few days away. At this time, it seems unlikely that the storm
track will shift far enough south to give us snow, but can not yet
rule that out with 100 percent confidence. The much more likely
location for snow with this system will be the Dakotas where
Christmas could be rather snowy.
This is a very dynamic system and some forecast models have us
seeing dewpoint into the mid 50s on Christmas day. This is
resulting in marginal instability that along with strong wind
shear and good upper dynamics may translate into a very rare
severe thunderstorm threat for portions of the central plains on
Christmas Day. At this time it is too early to pin down most
favored location for severe thunderstorms and will have to see how
the storm ultimately tracks.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday evening)
Issued at 454 PM CST Tue Dec 20 2016
VFR conditions are forecast through the TAF period. Look for winds
to increase by mid day Wednesday behind a cold front. Wind gusts
around 25kts are possible through the afternoon. Clouds will be
limited to mid and high levels.
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1024 PM EST Tue Dec 20 2016
High pressure will dominate the region with warm temperature
through Wednesday. On Thursday, a clipper system will bring light
snow to the area followed by high pressure through Saturday. A
cold front Saturday night will pass threw the region, but near
normal temperatures and dry weather is expected for Christmas.
.NEAR TERM /THROUGH TONIGHT/...
Update...Minor changes to the forecast to account for latest
Previous discussion...Shallow shortwave passing by to the north
will drive a weak frontal boundary through the region overnight.
High clouds ahead of this system currently pushing in from the
west and will be around through the evening hours before pushing
east after midnight. Return flow around high pressure east of Cape
Cod also throwing some low level moisture into coastal zones. As
boundary layer winds turn more westerly overnight expect this
moisture to affect mainly midcoast areas this evening before
Expect clouds to move into northern zones after midnight and a few
snow showers may enter the picture toward Wednesday morning. Lows
overnight will range through the single numbers north and through
the teens south.
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
Update...I have adjusted PoP Wednesday night based on latest model
guidance. Models are showing a modest burst of isentropic lift
ahead of clipper system slicing thru the forecast area after 06z.
So PoP now ramps up towards likely by 12z.
Previous discussion...High pressure will build south of the
region on Wednesday. Increasing upslope flow and lingering low
level moisture will keep clouds and low chance pops for snow
showers in the forecast through the morning hours in the north.
Expect diminishing clouds in the afternoon. Elsewhere partly to
mostly sunny skies will prevail. Highs on Wednesday will top out
slightly above normal with readings in the upper 20s to mid 30s
north and mid 30s to lower 40s south.
High pressure will push offshore Wednesday evening as weak low
pressure approaches from the west. Expect increasing clouds during
the evening and light snow will over-spread the region from west
to east through daybreak. Expect any accumulations in the south to
be light and spotty. Mountains and foothills may pick up an inch
or two by morning. Overnight lows will generally bottom out in the
lower to mid 20s.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
An Alberta Clipper system will move through the region from the west
on Thursday and will produce light snowfall across most of the area,
which will affect the morning commute and last through the day. The
clipper that moves through the area on Thursday will live up to
its reputation in being fast moving with light precipitation
amounts. Although it is a sharp shortwave trough that will drive
this system, there will not be a strong moisture connection
available with it. Generally expect 1 to 3 inches of snow for most
of the area. The coastal and island area will see snow mixed with
rain at times, which will limit their snowfall totals to around 1
inch or less.
High pressure will build in from the south and bring westerly flow
behind the system on Friday. We will see an influx of warmer
temperatures through Saturday. A cold front will pass through the
region Saturday night with colder air moving into the region.
Christmas day will be dominated by high pressure and temperatures
from the upper 20s in the mountains to the upper 30s to low 40s
along the coast and islands.
High pressure crossing the area Christmas night will bring a chance
for good radiational cooling. Both the GFS and ECMWF are in pretty
good agreement on this, though the raw model forecasts which go into
our blends do not do well on these nights, especially as
temperatures begin to warm aloft by morning. Because of this, the
best approach seemed to be to blend the SuperBlend of models with
the much colder MEX which would be expected to perform better in
radiational cooling due to its use of statistical adjustments. Some
high level cirrus clouds may move in from the west by morning, but
this may not be enough to keep temperatures from dropping into the
teens and single digits.
GFS and ECMWF are in broad agreement on a large trough which is
forecast to move into the Western United States later this week and
tack through the Northeast early next week. But there are still
differences in how fast and how much precipitation we will see
from this system. The GFS is the fastest solution that has
precipitation starting on Monday afternoon to evening and exiting
our region by Tuesday morning. The ECMWF has precipitation
starting Monday evening as shower and then steady precipitation
would not start to Tuesday morning and exit the area until
overnight Tuesday. Precipitation type may be a bit of a question
with this system, but there is too much uncertainty in the various
possible tracks to put too much detail into the forecast at this
time. For now will go with mostly snow, changing to rain in
The climate outlook over the next few weeks is supported by the
expected positive NAO and AO outlooks. This gives us a pattern
dominated by chance of above normal temperatures and precipitation
through week 2, ending on January 2nd.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Update...No major changes to previous aviation forecast. 00z GYX
raob indicates modeled LLWS is being observed pretty close to
forecasts. Recent HRRR runs seemed to be handling the current
winds aloft the best...so I patterned TAF LLWS timing after its
Summary: High pressure just southeast of the region will continue
to drift east as a weak disturbance passes north of the region on
Wednesday. Another low pressure system will approach the region by
Restrictions: VFR conditions should dominate through Wednesday night
outside of a few caveats. First...southwest flow this evening will
likely bring MVFR clouds and a few flurries/shsn to RKD...with a
lower potential of this happening at PWM and AUG. By Wednesday
afternoon...MVFR shsn are possible at HIE...but expect the majority
of restrictions to occur after 18Z Wednesday. Light snow will
approach HIE/LEB as high clouds thicken/lower towards daybreak
Winds: Light southerly winds /less than 10 kts/ will become westerly
by daybreak Wednesday and increase to 10g16kts. Winds will shift
back southwest and diminish to less than 10kts Wednesday night.
LLWS: 2kft winds will increase to 30-35kts from the southwest this
evening...with LLWS resulting. This will end by daybreak
Long Term...MVFR to IFR conditions are expected on Thursday.
Generally VFR, conditions expected through Saturday night. Will not
rule out MVFR in the mountains through early Friday morning.
Short Term...Continuing SCA`s from late this afternoon through
early Wednesday morning.
Long Term...Small craft are expected through most of the long term
with flow from the southwest to west through the weekend. Flow will
start to switch northerly late Sunday into Monday across the Gulf of
Maine. Wave heights are forecast to be 5 feet or less, except on
Saturday night with wave heights ranging from 4 to 8 feet with
the passage of the cold front.
MARINE...Small Craft Advisory until 7 AM EST Wednesday for ANZ150>154.
Area Forecast Discussion
National Weather Service Jackson MS
558 PM CST Tue Dec 20 2016
Updated for 00Z aviation discussion
00Z TAF discussion:
Will be watching for regeneration of stratus and fog later tonight
into early Wednesday, however, conditions may not be quite as
favorable with a considerable amount of altocumulus streaming over
the area now from the west. These clouds will disrupt cooling some
and this could be enough prevent fog formation in many areas.
A stratus deck lurking over AL is poised to expand westward again as
it did last night, so have stayed fairly pessimistic with the
forecast and more reflective of the HRRR in showing IFR ceilings in
the GTR-MEI-HBG corridor. The HRRR is not as far west as last night
with the stratus and have left the GWO-JAN/HKS corridor out of
forecast restrictions for now. Otherwise, expect dissipation of any
stratus/fog by noon Wednesday with VFR conditions expected areawide
during the afternoon. /EC/
Tonight into Wednesday: The pesky low stratus deck continues to
slowly erode eastward toward the AL border this afternoon. It is
expected to continue to mix out over the next few hours, providing
at least temporary clearing in the east. Winds will be calm/very
light and the sky will remain mostly clear, allowing temps to fall
off quickly again after sunset.
With dewpoints remaining in the 30s over the eastern portion of the
area, dewpoint depressions will likely dwindle to near zero
overnight, thus fog will again become possible late tonight into
early Wednesday morning. The freezing line is expected to be near I-
20, so there will again be potential for freezing fog over the
northeast quarter of the CWA. High res models also suggest
sufficient low level moisture remains for the redevelopment of a
shallow layer of very low stratus over the eastern half of the area.
There remains some uncertainty as to whether the stratus might
interrupt fog potential, or if both stratus and fog would exist as
was the case this morning. For now, patchy freezing fog wording has
been added to the forecast for the NE 1/4 for late tonight/early
Wed, with plain old patchy fog over the SE. Later shifts will
continue to assess whether dense fog or freezing fog concerns need
to be addressed in the HWO/graphics. Otherwise, Wednesday will be a
warmer day as surface flow kicks back around to the south ahead of a
weak quick-moving front. /DL/
Wednesday night through early next week...
Temperatures should remain above the freezing mark on Wednesday
night as return flow from a surface high over the SE Coast of the US
pulls warmer air into the region. A weak upper level disturbance
embedded within zonal flow aloft and it`s attendant cold front will
push through the ArkLaMiss on early Thursday morning. This front is
expected to remain mainly dry, however the NAM and Euro try to
develop some light shower activity as moisture increases ahead of
the front in the southern reaches of the Pine Belt. Slightly cooler,
drier air associated with a broad area of high pressure will begin
to filter into the region from the west behind the front.
Temperatures will be near average on Thursday and will increase 1-2
degrees on Friday as the high progresses eastward.
A more active weather pattern will begin to shape up for late Friday
and through early next week as a more significant upper trough
begins to lift from the Gulf of California through the SW US and
finally into the Midwest by Sunday. Models still disagree quite a bit
on the timing of this feature with the GFS still lagging behind the
Euro a few hours. Models are also in agreement that an even more
potent upper low will begin to cross the Rockies on Sunday. These two
systems will have several impacts on our region`s Holiday forecast.
Light showers will first become possible on Friday night as warm air
advection picks up and the first upper disturbance moves north of
area. Continued warm air advection on Christmas Eve and Christmas
Day will result in temperatures 10 to 20 degrees above normal.
Christmas day will be the warmest day of the period with 850mb temps
increasing to between 12-16 degrees, abnormally high for this time of
year. This will result in high temperatures near the surface in the
mid 70`s. Highs on Christmas 2016 could even rival the highs of Christmas
Day 2015 when we reached 80 degrees in Jackson if we can remain dry
enough to allow radiational heat to make more of an impact.
A surface front associated with the second storm will progress
through the region early next week, however the ArkLaMiss will stay
far enough from the significant dynamics associated with this closed
low to limit any severe weather potential.
.PRELIMINARY POINT TEMPS/POPS...
Jackson 33 61 46 59 / 0 0 9 7
Meridian 32 60 45 61 / 0 0 13 8
Vicksburg 29 61 44 57 / 0 0 6 6
Hattiesburg 35 63 50 64 / 0 0 18 11
Natchez 36 62 46 59 / 0 0 9 7
Greenville 29 55 38 51 / 0 0 8 4
Greenwood 28 57 38 54 / 0 0 8 4
Area Forecast Discussion
National Weather Service Memphis TN
550 PM CST Tue Dec 20 2016
Update to adjust evening cloud cover and lower temperatures
Arctic high pressure remains centered over the eastern portions of
the Mid South this evening. Low stratus has eroded away across the
eastern areas with clear to partly cloudy skies expected areawide
through the rest of this evening. Temperatures have plummeted
across eastern sections to forecast lows...therefore have dropped
low temperatures several degrees in these locations.
Freezing fog should again redevelop over the eastern half of the
forecast area by late evening and persist through early Wednesday
morning. Areas of dense freezing fog will also be possible and
will continue to monitor for a freezing fog advisory and hazardous
travel later tonight.
Low stratus should also redevelop in these locations by morning
and persist until late morning before mixing out.
Updated forecast and grids will be sent shortly.
.PREV DISCUSSION... /issued 343 PM CST Tue Dec 20 2016/
Afternoon GOES Visible imagery showed low stratus had eroded over
west TN and northeast MS. Surface analysis showed mid 30s dewpoints
over these areas, while lower and mid 20s dewpoints prevailed
along and west of the MS River. Given the weak low level pressure
gradient and limited high clouds, freezing fog will again be
possible east of the MS River late tonight. Recent HRRR model
runs concur. Will carry a mention of locally dense freezing fog in
the Hazardous Weather Outlook. Advisories for freezing fog will be
issued, if needed, by the evening and overnight shifts.
Otherwise, mild and fair weather to prevail over the Midsouth into
the late portion of the week, under building upper level heights.
A shortwave trof will lift out over the building Gulf coast
ridge, into the Ozark plateau. There was still a fair bit of
model disagreement with respect to timing on this feature, but
the more progressive ECMWF and Canadian models were in better
agreement. With that in mind, have include showers for Friday
along and north of the I-40 corridor.
For the Christmas holiday weekend, a low level warm sector will
build over the Midsouth under strengthening southwesterly flow
aloft. Some warm advection showers possible Christmas Day, but
better rain chances will arrive Christmas night and Monday, with
the approach of a cold front. The main upper low will track across
the northern plains, and present quiet a variety of winter weather
over the plains if the models verify. For the Midsouth, mild and
occasionally wet weather will prevail over the Christmas holiday
VFR at MEM and JBR...with a period of LIFR/IFR from low stratus
and freezing fog overnight at TUP and MKL. Light/Calm winds will
become south at 6-8kts after sunrise.
Area Forecast Discussion
National Weather Service Raleigh NC
845 PM EST Tue Dec 20 2016
A frontal zone will push off the Southeast coast tonight, as high
pressure builds in from the north. This high pressure will hold over
the region through Wednesday night, then push to our south as a cold
front approaches from the northwest on Thursday.
.NEAR TERM /THROUGH TONIGHT/...
As of 845 PM Tuesday...
The clearing line currently bisects the forecast area from NE to SW,
cutting through the Triangle area, easing to the SE as the 850 mb
trough shifts through the region. Its movement thus far this evening
has been depicted fairly accurately by the HRRR and WRF-ARW, and
these have been used to shape the forecast progression of the
clearing for the remainder of the night. In short, the entire
forecast area should be mostly clear prior to 09z, with only a few
high clouds, located on the south end of the mid level speed max
crossing the Great Lakes/Northeast, marring an otherwise clear sky.
The surface ridge will continue to nose into the area while its
center nears the southern Appalachians, all of which will lead to
very light winds or calm surface air, facilitating radiational
cooling, particularly in the outlying rural areas. Expect lows of 24-
32, warmer in the urban areas. -GIH
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 230 PM Tuesday...
Wednesday, sfc high will settle overhead while the flow aloft
remains zonal. Aside from a few patches of cirrus expect sunny skies
and moderating temperatures. MOS guidance depict little variation,
suggesting a high likelihood of high temperatures in the mid 50s.
Wednesday night, an increase in mid-high level cloudiness will
occur, particularly after midnight, as a s/w in the flow aloft
approaches from the west. The development of a lee side trough may
also cause the near sfc wind to stir, mainly in the western Piedmont
after midnight. The combination of increasing cloud cover and weak
stirring of the sfc wind will result in overnight temps several
degrees warmer than the previous night. Min temps low-mid 30s.
Thursday and Thursday night, a sfc cold front associated with the
mid level s/w will cross central NC late Thursday and Thursday night.
While patchy cloudiness will proceed the front, appears that the
moisture and lift are too limited to generate any showers. May see a
sprinkle or two, mainly south and east of Raleigh, otherwise the
frontal passage expected to be dry. Southwest flow ahead of the
front along with partial sun should allow temperatures to recover
into the 55-60 degree range. Clouds will depart/diminish Thursday
night as nw flow behind the front ushers in a drier cooler air mass.
Overnight temps upper 20s nw to the lower 30s se.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 225 PM Tuesday...
There are significant differences between the models with respect to
timing (GFS is quicker than the ECMWF) of an upper level shortwave
disturbance over the weekend and subsequent upper low developing out
west and moving east toward NC through the middle of next week. As a
result, confidence in the timing of precipitation this weekend is
below average. However, there will probably be some light rain
somewhere over Central NC this weekend, but for now amounts appear
to be minimal. At the surface, the high over NC on Friday will shift
offshore and give way to ridging southward into the area from
Canadian high pressure. The strength of the ridge is uncertain, thus
the temperatures are also uncertain. Generally, expect slight
chances for precip (best chance on Saturday), and temperatures
steadily increasing from Friday (highs in the low 50s and lows in
the low 30s) through Monday (highs in the low to mid 60s and lows in
the mid to upper 40s).
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 640 PM Tuesday...
24 HOUR TAF PERIOD: Mainly MVFR ceilings across the area at this
time except for the NW piedmont where VFR conditions have remained
in place for much of the day. The edge of the MVFR ceilings is
clearly visible on satellite imagery and this is expected to
gradually move off to the east tonight. The HRRR model has picked
upon this fairly well and is showing a progression that has all
sites free of MVFR ceilings by 6z Wednesday morning with KRWI being
the last site to clear out. From this point on, expect VFR
conditions through the remainder of the TAF period with mainly light
and variable winds with predominant light northerly flow at times
during the afternoon hours.
LONG TERM: VFR conditions will be likely for the next several days
as high pressure remains in control of the weather pattern.
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Wednesday)
Issued at 334 PM CST Tue Dec 20 2016
Fast, nearly zonal flow aloft remains in place over the northern and
central portions of the CONUS with areas of cirrus crossing the
region. Shortwave trough the passed to the north overnight brought a
weak front into the area but pressures were already falling
quickly from Kansas into the western Dakotas as the next wave enters
the Pacific Northwest. Only weak cold air advection into the morning
and some insolation has allowed for a much warmer day today as the
old Arctic airmass continues to modify. From what can be seen in the
holes in the cirrus, the snow field from the weekend snowfall was
The boundary layer continues to present the greatest forecast
challenges tonight and Wednesday, keeping this a low confidence
forecast. Models continue be too greatly impacted by the diminishing
snow field, with the NAM seeming to hold on to it through the length
of its 12Z and 18Z runs. Wind speeds look fairly light this evening
with some increases above the boundary layer late in the night as
the next modified cold front approaches. Satellite and models
suggest scattered cirrus should continue to pass overhead but
clearing a bit late into night into Wednesday. Dewpoints have risen
well into the 20s in much of the area, and with the light winds and
at least some clearing, could see fog develop particularly over any
areas that are still snow covered. RAP and HRRR do seem a bit too
quick with visibilities falling right near sunset however. Will go
ahead with patchy fog mention this evening into the post-sunrise
hours of Wednesday for all but the highest terrain but much will be
determined by hour-to-hour trends. Have again discarded the straight
NAM temperatures for highs but still have little confidence in temps
with good overnight warm air advection tonight followed by CAA
during the day Wednesday, some cirrus likely continuing, perhaps
some snow yet to melt off and the fog potential. Have raised values
a bit based on today`s warm temps here and upstream.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 334 PM CST Tue Dec 20 2016
The biggest take away from the extended period is much warmer
temperatures for the holiday weekend.
The first mention of PoPs return Friday morning in the form of rain
and snow. Model guidance is still inconsistent with the timing of
the weak lead wave. The EC and Canadian are the fastest and furthest
north with the wave, while the NAM and GFS are further south.
If model guidance continues to trend towards warmer surface
temperatures, the mention of snow may be taken out in future
forecasts. Surface temperatures warm into the low 40s Friday
afternoon, transitioning any remaining precip to all rain. Warm air
advection showers/thunderstorms are possible Saturday night into
early Sunday morning, ahead of the main mid-level trough.
The main mid-level trough is expected to eject into the central
plains on Christmas Day Sunday. Run-to-run model consistency
continues to track the surface low from northwest Kansas into
central Nebraska, keeping the forecast area within the warm sector.
Decent model agreement with surface dew points surging into the 50s
and high temperatures in the upper 50s to near 60 degrees ahead of
the front on Sunday. These dew points coupled with modest ML lapse
rates equate to MUcapes in the 300 to 500 J/KG during the afternoon.
Shear parameters are also quite impressive for this time of year
with 0-6 KM bulk shear near 50-60 knots and 0-1 KM near 30 knots.
Therefore have mention of thunderstorms during the afternoon into
the evening. Quiet weather is expected to prevail for the remainder
of the period.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 521 PM CST Tue Dec 20 2016
With melting snow and light winds this evening and overnight,
could see some patchy haze or fog across the area. Otherwise
conditions remain VFR for the day tomorrow with a wind shift late
in the forecast period.