Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/06/19
Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
606 PM MST Tue Mar 5 2019
.UPDATE...
Freezing fog has developed around KLVS again this evening, so have
added FZFG to the Wx grid tonight and have also updated the sky grid
based on current trends. It`s unclear how long the fzfg will last as
winds will vary from SSE (which would favor it persisting) to SSW
(where the downslope component should help eradicate it). Will
monitor for a bit before deciding on a Freezing Fog Advisory.
Regardless of visibility, any freezing fog can be dangerous, and
those in the area should use caution. ZFP already out.
34
&&
.PREV DISCUSSION...447 PM MST Tue Mar 5 2019...
.AVIATION...
00Z TAF CYCLE
Though the low clouds across eastern NM shrunk in coverage somewhat
this afternoon, a batch remains over EC NM and this batch will be
moving back over KLVS at any moment. It is expected that IFR/LIFR
cigs at KLVS will persist through the overnight hours. Do not expect
a repeat of FZFG at KLVS tonight, but only moderate confidence
exists. Low clouds have just barely cleared out over KTCC, and it is
expected that they will not fill back in tonight, though confidence
is lower here. Otherwise, VFR conditions are expected at remaining
TAF sites. High clouds will continue to stream over northern NM
overnight. Southwest winds will increase on Wednesday, with gusts
near 30 kts likely across much of western NM and along and just east
of the central mountain chain. These winds should help clear out any
remaining low clouds across eastern NM by mid morning.
34
&&
.PREV DISCUSSION...300 PM MST Tue Mar 5 2019...
.SYNOPSIS...
Stubborn low clouds over east central New Mexico will continue to
slowly erode tonight while mid to high level clouds move from west
to east over the north. Overnight low temperatures will be warmer.
A storm system passing to the north of New Mexico will bring rain
and high elevation snow to the northwest and north central Wednesday
through Thursday along with windy weather Thursday afternoon.
Another storm system will bring strong winds, rain and high
elevation snow to most of northern and central New Mexico Friday
into Saturday. Daytime temperatures will finally rise above average
Wednesday through Friday but dive 5 to 10 degrees below normal
Saturday. Another relatively wet storm system is possible early next
week.
&&
.DISCUSSION...
An area of low clouds over east central New Mexico continues to
slowly erode this afternoon. The HRRR indicates this trend will
persist but some low level moisture may pile up along the east
slopes/highlands from the Springer area to Raton and along the
Colorado border east of Raton this evening before it`s finally done.
Overnight low temperatures to be warmer nearly everywhere in the
forecast area.
A storm system passing to the north of New Mexico will bring rain
and high elevation snow to the northwest and north central starting
Wednesday and continuing through Thursday.
Potential for a few lightning strikes Wednesday northwest and north
central but NAM12 expands the potential areal coverage and
instability Thursday. Did not include any thunderstorms in the wx
grids with this package but later shifts may decide to if model
trends persist. Snow amounts in the San Juans may reach 4-8 inches
above 8000 feet by late Thursday, with the majority of it
accumulating Wednesday night. Therefore holding off on issuing an
advisory for now. Winds to strengthen Thursday, becoming strongest
along and south of Interstate 40 and along and east of Interstate 25
and may reach speeds that would trigger issuance of wind advisories.
Another storm system crosses New Mexico from west to east Friday and
Friday night bringing rain and high elevation snow to most of the
forecast area. In addition, strong winds are forecast to become more
widespread Friday, when there is potential for localized damaging
wind speeds especially from the south central to the east central.
Northwest winds look to be quite strong Saturday from the central
mountain chain over much of the east as the storm departs.
Daytime temperatures warm to above average Wednesday through Friday,
with an assist by the strong downslope winds. A backdoor front may
flirt with the far northeast Thursday/Friday which could raise havoc
with temperatures but the 18Z NAM12 has backed off on the
southwestward progress the 12Z run suggested.
Another relatively wet storm system is forecast for early next week.
&&
.FIRE WEATHER...
...CRITICAL FIRE WEATHER CONDITIONS THURSDAY EAST CENTRAL PLAINS AND
POSSIBLY THE LOWER RIO GRANDE VALLEY...
The Arctic airmass across the eastern plains is modifying rapidly
this afternoon and a warming trend is underway areawide that will
continue through Thursday most areas and send temperatures back
above normal by Wednesday. Increasing westerlies Wed/Thu in advance
of a potent Pacific trough will result in critical fire weather
conditions by Thursday afternoon across portions of the eastern
plains as well as portions of the lower Rio Grande Valley.
Even stronger winds will develop Friday in advance of the Pacific
trough, but moisture will increase and humidity will not exceed
critical threshold. The Pacific trough will bring cooler
temperatures and chances for wetting precipitation through Saturday
morning, mainly to the mountains and surrounding highlands. Strong
winds will persist Saturday behind the exiting trough, especially
across the eastern plains where humidity may also exceed critical
threshold. However, Haines values of 2-3 and temperatures at or
below normal will limit critical fire weather conditions Saturday.
Look for a break Sunday followed by a wetter system early next week,
which may bring good chances for wetting precipitation to much of
the area.
11
&&
.ABQ WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Thursday afternoon through Thursday evening
for the following zones... NMZ108.
&&
$$
34
Area Forecast Discussion
National Weather Service Boston/Norton MA
902 PM EST Tue Mar 5 2019
.SYNOPSIS...
Unseasonably cold but mainly dry weather will prevail through
Thursday with slowly moderating temperatures Friday. High
pressure builds to the north Saturday, then a strong storm
moves through the Great Lakes Sunday which will likely bring
a period of rain to the region, possibly starting as a wintry
mix in the interior. Drier air moves in behind the storm on
Monday.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
9 PM Update...
Forecast is in good shape. Cold front is making its way through
western New England and should be moving offshore by 06Z or so.
There are a few snow showers in the Catskills which may make the
trip over the Berkshires per high-res guidance, but probably not
much farther than that with relatively weak winds at lower
levels and a dry airmass in place. That said, HREF and HRRR
point toward possibility of scattered snow showers redeveloping
around outer Cape just after midnight due to some ocean
enhancement. Forecast has this all handled well so no major
changes made.
Cold advection brings 850 mb temps down to -18 to -20C by
morning. Lows will be mostly in the teens with some single
numbers of the higher terrain in MA. Wind chills by morning in
the single numbers, dropping below zero over higher terrain.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday...
Mid level trough axis and core of coldest air aloft will be
over New Eng. Sunshine in the morning, then expect diurnal cu
to develop late morning into the afternoon. Dry weather
expected but can`t rule out a few flurries in the higher
terrain. 850 mb temps around -18C so highs will be mostly in
the 20s, with upper teens in the Berkshires. Gusty NW winds
with gusts to 25-30 mph will add to the chill.
Wednesday night...
Shortwave trough axis moves offshore, but a secondary shortwave
will be approaching from the NW which will reinforce arctic
airmass across New Eng. Mainly dry weather expected but
continued very cold. Lows will be mostly in the single numbers,
with teens near the coast.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
This portion of the forecast will likely feature a pair of mid
level cutoffs within the northern stream of the mid level flow,
and a nearly zonal flow over the southern USA much of this week.
Then the pattern will hinge upon how much energy can move into
the base of the western trough, and the resulting amplification
within the northern and southern streams. This will not only
impact the strength of a low pressure expected to develop over
the Plains states late this weekend, but how quickly our region
will warm up. 05/12Z guidance is in reasonable agreement for
this time range, but there is enough variance to not set the
forecast details in stone just yet.
Mainly dry weather in store for southern New England into
Saturday. A low pressure is expected to pass well south of our
region Saturday. This may have enough reach to impact the outer
southern coastal waters with some rain, but there is an even
lower risk for precipitation on the islands. Will need to
monitor this track closely over the coming days.
Our next chance for more substantial precipitation looks to be
sometime late Saturday night into Sunday night as a low pressure
moves into the Great Lakes. Depending upon the exact timing,
there could be some snow of the front-end, which then
transitions to rain during the day Sunday before ending Sunday
night.
Temperatures should remain below normal through Saturday night,
then trend to near to above normal by Monday into Tuesday.
&&
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Wednesday Night/...High confidence.
Tonight...
A period of VFR cigs 4-6k ft, clearing late. Isold -SHSN,
mainly north of the Pike. Wind shift to NW with gusts to 20 kt
developing along the coast after midnight.
Wednesday...
VFR with sct-bkn cigs around 5k ft developing in the afternoon.
NW gusts to 25 kt.
Wednesday night...
VFR with diminishing wind.
KBOS Terminal...High confidence in TAF. Low risk for a -SHSN
between about 05-08Z. Little to no accumulation.
KBDL Terminal...High confidence in TAF.
Outlook /Thursday through Sunday/...
Friday through Friday Night: VFR. Breezy.
Saturday: VFR.
Saturday Night: VFR. Breezy. Chance SHSN, slight chance FZRA.
Sunday: MVFR/IFR conditions possible. Breezy. SHRA, chance
SHSN, slight chance FZRA.
Sunday Night: Mainly VFR, with local IFR possible. Windy with
local gusts up to 30 kt. Slight chance SHRA, chance FZRA.
Monday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Wednesday Night/...High confidence.
Winds already reaching 25kt on outer south coastal waters per
buoys and on Nantucket Sound per recent ferry report, so moved
up timing of SCA for these areas. Otherwise, cold front moves
through late tonight with surge of gusty NW winds late tonight
into Wednesday, with SCAs going into effect on remainder of
MA/RI waters. Winds slowly diminish Wed night. Areas of
freezing spray developing on the open waters late tonight into
Wednesday evening.
Outlook /Thursday through Sunday/...
Friday: Winds less than 25 kt.
Friday Night: Winds less than 25 kt. Slight chance of rain.
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of rough seas. Rain showers, chance of snow
showers, slight chance of freezing rain.
Sunday Night: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Rough seas up to 10 ft. Rain showers.
Monday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Rough seas up to 9 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 4 AM Wednesday to 5 AM EST Thursday
for ANZ232.
Small Craft Advisory from 4 AM Wednesday to 1 AM EST Thursday
for ANZ231-233>235-237-251.
Small Craft Advisory from 4 AM to 7 PM EST Wednesday for
ANZ230-236.
Small Craft Advisory from 4 AM Wednesday to 7 AM EST Thursday
for ANZ250.
Small Craft Advisory until 7 AM EST Thursday for ANZ254>256.
&&
$$
SYNOPSIS...Belk/KJC
NEAR TERM...JWD
SHORT TERM...KJC
LONG TERM...Belk
AVIATION...Belk/KJC
MARINE...JWD
Area Forecast Discussion
National Weather Service Caribou ME
1040 PM EST Tue Mar 5 2019
.SYNOPSIS...
An upper level disturbance will cross the area overnight into
Wednesday. High pressure builds Wednesday night into Friday.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
1017 PM Update...
Hrly temps/dewpoints were adjusted once again to fit the latest
conditions. Temps have dropped off quickly w/the latest arctic
airmass settling across the region. Temps back across NW Maine
are down to -6 at Clayton Lake(K40B) as of 1015 pm. Presque Isle
came in w/-2F. Single numbers elsewhere across northern areas
w/lower teens in the central and downeast areas. Decided to
lower temps more in the low lying and sheltered areas overnight.
Disturbance seen on IR satl imagery moving e across southern
Quebec. At the sfc is weak low pres that coincides w/the upper
disturbance. Some light returns showing up in southern Maine.
HRRR and the latest RAP show some light snow developing
overnight across the central and downeast areas and then trying
to edge newd by Wed morning. The daycrew`s assessment looks in
line and did not change the precip chance w/this update.
Previous Discussion...
Clearing skies this evening will promote quick radiational
cooling this evening, but will slow in southern zones later
tonight as clouds thicken from the west. An upper level trough
will approach from Quebec overnight and amplify. This will
induce weak cyclogenesis on the cyclonic side of the upper
trough in the Gulf of Maine. As this occurs, a brief period of
snow will develop across the southern half of the forecast area.
Any snowfall amounts will be less than an inch and confidence
is not high enough to assign even likely pops at this time.
Further north, the radiational cooling will continue through the
night and will yield subzero readings by daybreak across
Aroostook County. Cannot rule out a few readings dropping
towards minus 15F in some of the usually colder locations of
northern Aroostook. Favored some of the coldest bias corrected
guidance in the forecast. For Wednesday, the big issue will
surface- based instability as the unusually cold upper trough
crosses the area. Steep lapse rates up to H700 and available
H850 moisture will produce SBCAPE over 100 J/kg at times. Snow
showers will be a threat across the entire area and some could
be briefly intense. The snow squall parameter is flashing the
best signals towards northern Aroostook County and the western
mountains, but can`t rule out a strong snow shower for Bangor on
Wednesday afternoon. Do like the idea of the strongest snow
shower activity in northern Aroostook as lift with the upper
trough will be best in that area. Used H850 temps as a guide for
Wednesday`s high due to the expected mixing. In terms of winds,
the synoptic scale winds pick up late in the day...mitigating
concerns about blowing snow. However, gusts will snow showers
could exceed 30 mph.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
High pressure at the surface will be moving off the Mid-Atlantic
coast Wednesday night as an upper trough lifts northeast of the
area. Any flurries and snow showers early Wednesday evening should
taper off as the air stabilizes. Otherwise, Wednesday night will be
partly cloudy. This will be followed by a partly sunny and very cold
day Thursday as the upper trough remains nearby to the northeast.
Thursday night will then be partly cloudy and very cold with high
pressure to our south. Dry weather is expected to persist through
Friday with high pressure south of the area and an upper trough
remaining over eastern Canada. Temperatures Friday will be a little
milder than Thursday but still about ten degrees below average for
this time of year.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
High pressure will build over the area Friday night into Saturday.
This will bring a bright, sunny and tranquil day on Saturday with
some moderation in temperatures during the midday and afternoon. The
high will slide east of the area Sunday as a large low pressure
system lifts north into the Great Lakes area. Sunday will likely
begin mostly sunny and tranquil. Clouds will then increase during
the day ahead of a warm front pushing east of the Great Lakes low.
Snow may spread into the area Sunday afternoon, likely changing to
rain Downeast as warmer air gets pulled north. A changeover from
snow to rain may push north Sunday evening, possibly reaching
northern areas by late evening. However, the occlusion will quickly
push through as the low, tracking to our northwest, pulls drier air
northward. This may end precipitation over the north before much
rain falls. Monday should then be cloudy to partly sunny and mild as
a corridor or mild air slides across the area with the dry
intrusion aloft. A cold front will reach the area Tuesday
bringing in moderately cooler air and a chance for some snow
showers under a cloudy to partly sunny sky.
&&
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
NEAR TERM: The prevailing condition will be VFR outside of
snowshowers. Snowshowers may cause IFR vis late tonight into
early Wednesday towards BGR and BHB. Shorter duration
snowshowers may affect all sites Wednesday afternoon, but vis
could temporarily drop to LIFR.
SHORT TERM: MVFR conditions north and VFR conditions Downeast
are expected Wednesday night. Conditions are expected to be
mostly VFR Thursday into Friday but may occasionally drop to
MVFR across the far north in lower stratocumulus clouds during
this period. VFR conditions in a mostly clear sky are expected
Saturday.
&&
.MARINE...
NEAR TERM: A Small Craft Advisory will likely be required by
Wednesday afternoon due to winds. Light freezing spray is
expected later tonight into Wednesday morning.
SHORT TERM: A SCA will likely be needed Thursday night into
Friday night for northwest to west winds gusting up to 30 kt.
Winds should diminish Saturday as high pressure builds over.
Winds should remain light into Sunday, but then may increase to
a SCA or gale late Sunday into Sunday night ahead of an occluded
front.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.
&&
$$
Near Term...Hewitt
Area Forecast Discussion
National Weather Service Hastings NE
549 PM CST Tue Mar 5 2019
.SHORT TERM...(This evening through Wednesday)
Issued at 334 PM CST Tue Mar 5 2019
Aloft: Moderately-amplified flow was over the CONUS per RAP
tropopause analyses and aircraft obs...with a trof over the E
Pac...a ridge over the Rckys...and a Hudson Bay low and trof over
the Ern USA. NW flow was over the Cntrl Plns with rising heights
as the ridge approaches. This ridge will crest over the rgn around
sunset tomorrow.
Surface: High pres was over KS. An Arctic front was over SA/MB.
The high will slide into AR/MO tonight on its way into the Gulf
Coast states tomorrow. The Arctic front will move SE thru
tomorrow...crossing the CWA in the afternoon. However...the
thermal contrast along tail end of the cold front will weaken. So
this front will be little more than a wind shift. Nrn Plns high
pres will build in behind the front.
Tonight: Mainly clear to start...but increasing clds espcly after
midnight. Should be m/cldy by dawn. Used consensus of all
guidance for lows which has been performing best over the last wk.
Wed: M/cldy. Not as cold...but still 15F below normal.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 334 PM CST Tue Mar 5 2019
Aloft: A weak/low-amplitude shortwave trof will move thru Wed ngt
into Thu AM. Heights will rise in its wake with the Wrn ridge
moving thru here Fri as a much deeper trof moves onshore into CA
and thru the Desert SW. The last 2 runs of the GFS/GFS-FV3/EC/
GEM/UKMET cont in unison on becoming negatively tilted with a low
forming over NEB Sat. Quite a bit of spread develops Sun. The GFS
/GFS-FV3 runs have cyclonic NW flow and troffing over NEB/KS while
the GEM/UKMET/EC runs maintain SW flow with a broad ridge as the
next deep low drops down the CA coast. This lowers fcst confidence
Sun-Tue.
Surface: Wed night the pres grad will increase as high pres drops
into the Nrn Plns and weak low pres ejects out of CO into OK.
Thu-Fri high pres will prevail over the Ern USA/Canada...and it
will extend back into NEB/KS. Lee cyclogenesis will occur Fri
afternoon. This low will cross KS from 12 AM-12 PM Sat. High pres
will build in Sun and probably slip E of the rgn Mon-Tue.
Temps: Contd much colder than normal...but not nearly as cold as
we`ve been experiencing. We will begin seeing a lot more 30s over
S- cntrl NEB and 40s over N-cntrl KS. Sat looks like temps will
finally climb above 32F at GRI...and all the other locations that
haven`t seen 32F since Feb 13th.
Precip: We are still expecting a band of 1-4" of snow mainly N of
I- 80 Wed night into Thu AM. The highest amts of 3-4" cont to be
expected from Ord-Greeley-Fullerton. Have initiated Situation
Reports (available top of our website) as probability remains high
we`ll need a Winter Wx Advisory.
Fri night-Sat: The EC/GEM/GFS cont in unison that there will be a
substantial warm nose with this sys. That means we are
advertising too much snow at the onset. Given that this sys is
still beyond 84 hrs...our fcst ptype algorithm conts to indicate
snow at the leading edge of the precip shield that moves in Fri
night. The more likely scenario is a mix of frzg rain/sleet
changing to rain Sat for most areas.
The mdl consensus is that a shield of mix precip will form and
move from SW-NE Fri night into Sat AM...with this trof rapidly
swinging thru with negative tilt. The upr low is fcst to close off
just N or E of the CWA. That means a quick shutoff to the precip
by midday Sat as the dry slot moves in. There are still a minority
of mdl runs indicating a low could close off over SE NEB. If that
occurs...that could prolong the precip into the afternoon E of
Hwy 281. But it`s doubtful there will be enough cold air around
for snow.
Rainfall amts cont to be of concern. The faster this sys moves
thru the better. Any substantive rain falling into such deep snow
will significantly increase its weight. That could stress
buildings with flat roofs to the point of partial failure/
collapse.
Snow will not be the dominant ptype this this sys. In fact...
there is potential we could see warning-level amts of frzg rain
(at least 1/4"). It has been so cold for so long...frzg rain could
even cont after air temps even climb above 32F.
Can`t rule out a couple rumbles of thunder Fri night-Sat AM over
the SE fringe of the CWA (Beloit-Hebron).
Suggest everyone cont to closely monitor this storm.
Winds: Incrsd winds above MOS Wed night. Have seen this many
times when E winds end up stronger than fcst as the pres gradient
tightens from high pres sinking into the Nrn Plns and a warm front
is stalled over KS/OK.
Sat night into Sun AM will be windy and the fcst probably doesn`t
fully reflect how windy it will be just yet. We`re probably
looking at 20-30 mph G40-50. If we get warning-level ice...this
could result in sct power outages from bringing down tree
branches.
Pattern: The EC/GFS/GEM ensemble means are all fcstg a major
pattern change in the 10-15 day time frame (Mar 15-20). The trof
that has persisted over the Wrn USA for the last 30 days appears
like it could be replaced by a ridge. That would mean temps
returning to near normal...and favoring above normal at times as
periods of downslope warming could occur.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday)
Issued at 539 PM CST Tue Mar 5 2019
VFR conditions are forecast. However, ceilings will develop and
lower as a shortwave trough approaches. Any ceilings lower than
VFR should hold off until just after the valid time of the
forecast.
&&
.CLIMATE...
Issued at 526 AM CST Tue Mar 5 2019
..Various notes on our ongoing remarkably-cold snap (for Grand
Island/Hastings, our two primary long-term climate data sites)..
SECOND-COLDEST OPENING WEEK OF MARCH VERY LIKELY:
- Based on observed data through these first few days and our
current official forecast through the 7th, both Grand
Island/Hastings are well on their way to enduring the 2nd-
coldest opening week of March on record. The top spot currently
belongs to 1960, when the first week averaged an incredible 28
degrees below normal at Grand Island, and 26 degrees below
normal at Hastings.
LONGEST STREAK AT-OR-BELOW FREEZING IN DECADES?
- Today will mark the 19th-consecutive day that both Grand Island
and Hastings will fail to climb above the freezing mark (32
degrees).
- Based on our official forecast, this streak of at-or-below
freezing days should last through at least March 8th (Friday),
which would bring it up to 22 days.
- The last time Grand Island (GRI) had a 22+ day streak of at-or-
below freezing was 26 years ago, with a 22-day stretch from Dec.
9- 30, 1983. The record-longest streak is 31 days from Jan.
22-Feb. 21, 1936.
- The last time Hastings (HSI) had a 22+ day streak of at-or-
below freezing was actually the record-longest streak of 30
days, way back from Jan. 23-Feb. 21, 1936.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&
$$
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Heinlein
CLIMATE...JCB/Pfannkuch
Area Forecast Discussion
National Weather Service Wilmington NC
919 PM EST Tue Mar 5 2019
.SYNOPSIS...
A dry cold front tonight will usher Arctic air into the region,
bringing a couple freezing mornings both Wednesday and Thursday.
Expect a warming trend into the weekend with increasing clouds
and chance of showers late Friday and again on Sunday ahead of
approaching cold front.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 930 PM Monday...We`re in the lull ahead of the secondary
arctic front which has recently moved through Charlotte,
Asheboro, and Greensboro where dewpoints are plunging into the
single digits. Light winds have allowed some impressive
radiational cooling to occur in the cool prefrontal airmass and
several spots across eastern SC (Georgetown airport, Conway,
Kingstree) are already down to freezing. Look for temperatures
to jump by 3-5 degrees when the front arrives simply due to
mechanical mixing of the boundary layer. Latest HRRR/RAP trends
indicate the front should move across our forecast area between
midnight and 2 AM. Temperatures should then fall due to cold
advection overnight through daybreak Wednesday.
I`ve made no additional changes to overnight low temps,
although I still have concerns that I may be too cold in spots
given the amount of boundary layer mixing anticipated to occur
in the post-frontal regime. Discussion from 630 PM follows...
Back edge of the dense low clouds is clearing off the South
Carolina coast now. However scattered clouds are expected to
redevelop between 9-11 PM as lapse rates steepen with the
approach of the mid level trough dangling southward from the
main low up in Quebec. The top of the moisture should extend to
near 8000 feet AGL where temperatures will be around -10C, which
means radar could pick up some virga flurries overnight.
Increasingly dry sub-cloud conditions are expected to evaporate
any snow before it makes it to the ground.
There may be problems with the 18Z GFS initialization of
excessive snow cover across the eastern Carolinas. This appears
to manifest itself as a very cold, moist boundary layer that
continues through the night. I`m actually discarding the GFS at
this time and am relying on other model guidance for
temperatures, and have therefore raised our forecast lows by
about 2 degrees across the board. Recent HRRR runs even indicate
I may need to add another couple degrees. Cold 850 mb temps
(-7C to -9C) arriving late tonight still appear to guarantee a
freeze, and no changes have been made to the freeze warning at
this time. -TRA
Discussion from 300 PM follows...
Upper trough axis upstream, slated to transit SE NC and NE SC
late tonight, will carry an impulse containing vertical
circulations, but limited moisture, mainly 3z-5z. Surface
dewpoint depressions of around 10 degrees should evaporate most
flurries and the air mass is too cold aloft for sleet. Even so,
a few `flurry sightings` late tonight should not be a complete
shock. GOES Day Cloud Phase channel, shows well the cumulus in
the base of trough dropping across snowpack in IA, IN, soon into
KY and ern TN.
`Freeze Warning` posted area wide, as even the beaches drop
near, or below freezing, as Arctic air spills in late tonight.
Temperatures to drop below freezing in most areas after 3 AM if
not a little sooner, rising slowly in cold sunshine early
Wednesday. Dewpoints to take a pronounced dip after 6z, reaching
the teens into daybreak Wednesday and min-RH Wednesday around
30 percent even in the chilly air mass. Moderate NW breezes
Wednesday morning in CAA, will produce wind chills in the lower
20s at school bus stops, and area-wide.
A Freeze Warning will be needed again for early Thursday, but
considerably less wind as the core of high pressure nears.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 PM Tuesday...Extended period will be very similar to
what has been happening for much of the winter. A strong mid-
latitude cyclone will emerge from the Southwest and lift across
the Plains into the Great Lakes. The mid-level pattern will
transition from progressive Sat to more amplified Sun and Mon,
lifting a front stalled in the area on Sat north of the area on
Sun. The cyclone will pass well northwest of the area Sun night
into Mon, dragging a cold front across the area and off the
coast. Modest cold advection setups Mon night and Tue as
modified Canadian high builds in.
-Temperatures above normal Sat through Mon.
-Cold advection later Mon and Mon night will drop temperatures
to near normal on Tue.
-Rain chances increase Sat as front lifts north through the
area but best chances will be later Sun in warm sector ahead of
the front.
-Potential exists for high shear/low CAPE severe event on Sun,
but confidence is low given large uncertainties.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 300 PM Tuesday...Progressive pattern through the period
with shortwave riding by on Fri. This will lead to an increase
in clouds and chc of pcp late Fri into Fri night. Ridge building
in for Saturday should provide drier weather, but models are
hinting at low clouds possible into Saturday as front drops down
from the north. This front will return north Sat night as next
shortwave drives a front eastward into the Carolinas. Warm and
moist air on Sunday with temps into the 70s ahead of cold front
should help to produce some showers. High pressure to follow
with westerly downslope flow behind front on Monday will keep
warm temps across the area until later in the day when deeper
N-NW advects cooler air into the area for Mon night into Tues,
bringing temps closer to normal. Overall expect temps near
normal to start and end the period, but running above normal in
warming through much of the period. Should see a fair amount of
clouds around with best chc of pcp Fri night and then again on
Sunday.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 00Z....Modified arctic air will spill into the region through
the overnight hours. There will be enough cold air advection to keep
the winds above 5 kts. A Northwest wind is in store for
Wednesday, with nearly clear skies.
Extended Outlook...VFR Wed through Sat.
&&
.MARINE...
As of 930 PM Monday...Offshore winds should veer north when the
arctic cold front pushes off the coast shortly after midnight,
with speeds increasing to 20-25 kt. Current forecast looks good
and no changes are planned overnight. Discussion from 630 PM
follows...
No significant changes are needed to the marine wind/wave
forecast at this time. Discussion from 300 PM follows...
Strong NW wind and cold air will make dangerous marine
conditions overnight and early Wednesday, especially offshore
with 5-6 foot seas and 30 kt gusts. NW wind waves will interact
with N waves of nearly equal wave periods of 5-6 seconds making
for a mess overall. Winds and seas to improve beginning late
Wednesday, and by Wednesday night, NW winds 8-13 kt and seas 1-3
feet, highest offshore. Dry this period so no visibility
restrictions expected.
Light northerly flow Thu will become southerly in the afternoon
and evening as high pressure to the north shifts offshore.
Gradient remains weak and southerly flow will remain under 10 kt
through Fri night. Weak front drops south across the early Sat
with light northerly flow setting up. Light winds and changing
direction will keep seas 2 ft or less Thu through Sat. Stalled
boundary slowly lifts back north Sun morning. Gradient starts to
increase as cold front approaches and southerly flow jumps to a
solid 20 kt. Small Craft Advisory headline may be needed later
Sun and Sun night. Development of southerly flow Sat night into
Sun coupled with increasing wind speeds will build seas to 3 to
5 ft by Sun morning with potential for 4 to 7 ft later Sun and
Sun night.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...Freeze Warning from 2 AM to 9 AM EST Wednesday for SCZ017-023-
024-032-033-039-054>056-058-059.
NC...Freeze Warning from 2 AM to 9 AM EST Wednesday for NCZ087-096-
099-105>110.
MARINE...Small Craft Advisory until 2 PM EST Wednesday for AMZ250-252-
254-256.
&&
$$
SYNOPSIS...III
NEAR TERM...08/TRA
SHORT TERM...III
LONG TERM...III
AVIATION...DL