Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/21/21
Area Forecast Discussion
National Weather Service Lincoln IL
730 PM CDT Mon Sep 20 2021
Issued at 715 PM CDT Mon Sep 20 2021
Thunderstorms along a cold front will bring rain to the majority
of central Illinois from tonight into early Tuesday morning.
Some of the storms may be strong, with damaging winds being the
primary threat. By sunrise Tuesday, the line of storms is
expected to be in eastern Illinois where showers may linger
through much of the day.
Issued at 730 PM CDT Mon Sep 20 2021
Broken line of thunderstorms stretches from west central Wisconsin
to south of Kansas City early this evening. Shear values this far
east are not especially impressive, but MUCAPE`s off the RAP model
are above 1000 J/kg with the line as it moves into western
Illinois later this evening, so some stronger storms remain a
concern. Latest HRRR brings the storms in a weakening mode to near
the Illinois River by 11-midnight and to I-55 around 2 am.
General PoP trends in the previous forecast are on track, but made
some minor adjustments over the next few hours for timing along
the leading edge.
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 314 PM CDT Mon Sep 20 2021
Central Illinois is currently in a lull of activity ahead of
tonight`s cold frontal passage. Convection is forming along the
front from northwest of Kansas City through central Iowa into
Minnesota. Expect this line to continue eastward through the
evening and overnight hours. Short term forecasts show the
greatest sfc-500 km shear in the post-frontal air mass, but
sufficient shear along the front for the possibility of some
severe wind gusts. In any case, most locations in central
Illinois should observe a few hours of moderate to heavy rainfall
in thunderstorms as the front moves through overnight.
On Tuesday, expect a cooler day behind the front, with skies only
gradually clearing out from west to east. Showers are expected to
continue into the afternoon primarily near and east of I-57.
The front has sped up a bit with this forecast, with the threat of
very heavy rainfall in eastern Illinois decreasing somewhat.
However, with precipitable water values of 1.5-1.8 inches in the
pre-frontal air, small differences in feature movement or timing
of individual cells could mean large differences in rainfall
amounts. Pre-frontal storms should be capable of high rain rates.
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 314 PM CDT Mon Sep 20 2021
The upper trough is expected to be nearly overhead on Wednesday
morning with breezy northwest winds and temperatures in the 60s
much of the day. Many model solutions close off the low and keep
the center near MI/IN/OH through about Thursday evening. As such,
precip chances will be slow to fade out completely, especially in
eastern/northern portions of the forecast area. The next short-
wave trough from the northwest may begin influencing Illinois
early on Friday per the WPC cluster tool, though the forecast
currently reflects a short-lived warm up Friday before cooler
temperatures return on Saturday. Warming temperatures and dry
conditions are expected through this coming weekend into Monday.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 602 PM CDT Mon Sep 20 2021
Short term concern will be with south winds gusting 20-25 knots
this evening, but focus shifts to incoming convection ahead of a
cold front. Timing of the line of storms brings it to near KPIA
toward 05-06Z, but a general weakening trend is expected as it
gets further east. Ceilings expected to drop below 2,000 feet as
the rain gets closer, then should be down to IFR levels as a cold
front pushes through central Illinois between 08-12Z. Winds will
shift to the northwest and still gust to around 20 knots much of
the day Tuesday. A slow improvement in ceilings is expected, with
VFR conditions possible by mid afternoon near KPIA, but MVFR or
lower lingering in eastern Illinois well into the afternoon.
Area Forecast Discussion
National Weather Service Lubbock TX
609 PM CDT Mon Sep 20 2021
VFR conditions will continue. However, strong northeasterly winds
will persist through the TAF period behind a cold front that has
passed through all the terminals late this afternoon. The
strongest winds are expected to be from mid-morning on Tuesday
through mid-afternoon on Tuesday.
.PREV DISCUSSION... /issued 221 PM CDT Mon Sep 20 2021/
At 120 PM a cold front was along a line from Clovis to Petersburg to
Paducah. The front continues exhibiting a southward movement despite
the hot and well-mixed air mass that it is moving into. Have
generally followed a slightly modified HRRR solution for the
continued movement of the front the remainder of the afternoon and
through early evening when it should be through the forecast
area. An isolated thunderstorm or two is not out of the question
from about 22Z to 02Z across the southeastern corner of the
forecast area near where the triple point will be. The pre-frontal
trough looks to have stalled as surface winds at Aspermont and
locations to the east have now backed toward south. This will keep
enough surface-based moisture in place to justify a slight chance
mention there through early evening. Surface high pressure
building in behind the front overnight will result in an increase
in wind speeds with the breezy conditions continuing after sunrise
Tuesday as mixing keeps higher momentum air turned over. Cold
advection behind the front will bring our first day with a cooler
than normal average temperature at Lubbock since August 29th. The
middle of the range in MOS values shaded just a bit upward is
favored for highs tomorrow given trends for much of the summer and
The main story for the middle of this week will be a pleasant
glimpse of fall-like weather conditions as we remain under
northwesterly flow aloft with slowly building upper level ridging
to our west. Surface high pressure will continue to build in from
the north on Tuesday evening, relaxing the surface pressure
gradient and allowing winds to weaken fairly rapidly by dusk,
becoming light and variable overnight. These light winds in
combination with a dry post-frontal airmass and clear skies will
set the stage for very efficient radiational cooling, allowing
temperatures to fall into the mid 40s to low 50s across much of
the area by daybreak Wednesday. A few typically cool higher
elevation spots near the TX/NM border may even dip into the 30s.
Wednesday will be a nearly perfect day weather-wise with
temperatures near 80 and clear skies.
Through the rest of the work week, temperatures will once again rise
to levels slightly above normal as upper level ridging gradually
builds eastward overhead. Even so, 500mb height rises will be
relatively subtle, and temperatures will consequently only max out
in the middle to upper 80s on the Caprock and lower 90s across the
Rolling Plains by Friday. Mostly sunny skies will dominate as dry
air remains firmly entrenched over the area. The upper level flow
pattern will begin to evolve late week as a shortwave trough will
split off from the mean flow over southwestern Canada and dive
southwestward on Thursday. This troughing will eventually form
into a cutoff low somewhere off the Southern California coast,
which will push upper ridging eastward over Texas. This evolution
will not dramatically impact our local weather aside from a slight
increase in afternoon high temperatures over the weekend as upper
ridging remains over West Texas. For now, there is a wide spread
in guidance regarding the evolution of the upper low. There is a
remote possibility depending on the eventual track and strength of
the low that better moisture may be ushered back towards our area
next week, resulting in cooler weather. Something to watch, but
all-in-all, expect another week of dry weather locally. /DWK
Area Forecast Discussion
National Weather Service Marquette MI
747 PM EDT Mon Sep 20 2021
.SHORT TERM...(This evening through Tuesday)
Issued at 405 PM EDT MON SEP 20 2021
A strong cold front currently analyzed form northeastern Minnesota
to southwestern Iowa per MSAS analysis and surface obs will push
eastward across the U.P. tonight in response to a mid-level strong
short wave embedded in southwesterly flow out ahead of a long wave
trough over the Northern Plains. Before that front gets here,
scattered showers are expected over the next few hours over the
central and eastern U.P. in response to a subtle mid-level short
wave moving northward through the flow atop a moist and marginally
unstable PBL. RAP shows a packet of isentropic lift on the 315 K
surface (around 600-650 mb) lifting northward across the eastern
U.P. over the next couple hours which will likely lead to an
increase in shower coverage. Despite visible satellite showing some
nucleating occurring, no lightning has been observed yet over our
area. However, have maintained a slight chance of thunder for this
round of showers through this evening.
Tonight, that cold front will plow across the U.P. with a line of
heavy showers and likely some thunderstorms, especially west half.
NAM shows MLCAPE rising to around 1000 J/kg this evening ahead of
the line (the GFS, as usual, shows less). There will be strong shear
thanks to a 40-50 kt LLJ overhead, including 0-3 km shear vectors
around 30-40 kts, but deep layer shear vectors are oriented mostly
along the front. That said, there could be just enough cell growth
off the front for isolated bowing segments within a larger broken
line of storms tonight, hence the SPC Marginal Risk for severe
weather, but with the front moving quickly eastward across the area
it will probably be hard to keep any storms discrete. Models show
instability waning somewhat overnight, but there should be enough to
maintain at least a chance of thunder all the way into tomorrow
morning when the front reaches the eastern U.P. This strong LLJ
overhead will also lead to yet another night of gusty downslope
winds along the Lake Superior shoreline with some 30 mph gusts
possible before the front arrives and winds veer around to WNW.
Tomorrow, 850 mb temps drop to around 2-3 C behind the front leading
to a much cooler day. In fact, the air aloft will be cool enough
that there will probably be some lake-effect clouds and rain showers
over the west half. The better chance for those showers will be in
the morning when there is enough remnant moisture behind the front
that upslope ascent will compensate for very marginal lake-based
instability. It will be breezy much of the day as well surface
pressure rises around 3-5 mb/3 hr behind the front and steepening
lapse rates in the CAA regime allowing some 20+ mph gusts to mix
down to the surface (30 mph over the Keweenaw and along the Lake
Superior shoreline east of Marquette). However, the pressure
gradient weakens quickly in the afternoon leading to a decrease in
wind gusts, especially after about 18z. The cool air aloft and
scattered clouds will keep temps nearly steady in the upper 50s to
low 60s, except in the mid 60s far south central.
.LONG TERM...(Tuesday night through Monday)
Issued at 340 PM EDT MON SEP 20 2021
Long term period continues to present a few opportunities for rain
showers, but also a couple of very nice days. Going into the
weekend, there`s still a good bit of uncertainity in the progression
of a system dropping southeast through Ontario and the Great Lakes.
Overall high temps through the period appear near to just above
normal for a majority of the period, with a few chillier nights
early in the period.
Starting off on Tuesday night, continued light CAA and midlevel
ridging extending across the Plains into the northern Great Lakes
should help clear out skies from west to east. This should allow for
raditional cooling to let much of the interior west to dip into the
mid-upper 30s. Elsewhere lows should buttom out in the 40s given the
delay in clearing or the moderating influnces of the lakes. Light
winds in the decoupled lower atmosphere could allow for some frost
formation, especially if lows exceed expectations.
Ridging will continue Wednesday and given 850mb temps progged to be
1-3C, daytime highs should top out near 60 or in the low 60s. Skies
are expected to be clear to partly cloudy, with some exceptions
being in the downwind of Lake Superior where some light lake effect
rain showers will be possible.
Elsewhere on Wednesday, the earlier week trough is expected to be
blocked by a building ridge off the east coast. Soon after, the
trough is expected to intensify as surface cyclogensis occurrs and
close off the upper level trough over the Ohio River Valley/central
Appalacihans. From there, the low is progged to lift
north/northeast. Models have come into fairly good agreement on this
evolution, but vary some on timing and placement. Overall, rain
showers associated with this system will be possible Thursday into
the evening hours, mainly in the east.
Upstream another shortwave is expected to dip south and reinforce
the broad troughing over eastern Canada. As expected, there`s still
notable differences among the guidance about whether or not another
closed low will develop over the Upper Great Lakes or remain an open
wave as it transits eastward. Depending on this evolution, there
could be a few opportunities for rain showers this weekend.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 747 PM EDT MON SEP 20 2021
Sharp cold front and associated shra/tsra will move across the area
tonight. Until fropa, expect LLWS at all terminals as 45-50kt low-
level jet translates across Upper MI. With the shra/tsra at IWD/CMX,
MVFR conditions will occur, followed by IFR to low MVFR as winds
shift to an upslope w to nw direction. At KSAW, abundant low-level
moisture and upslope flow will result in IFR cigs until fropa. MVFR
cigs will then prevail at all terminals thru at least Tue morning.
While IWD/CMX should improve to VFR in the aftn as cloud bases lift,
KSAW may remain MVFR thru the day.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EDT MON SEP 20 2021
Tonight, a strong cold front will pass across the lake. Out ahead of
the front, southerly winds could reach gale force for a few hours
over the north central and eastern lake. Issued a Gale Warning
through midnight for the potential for southerly gales, but
confidence is not overly high thanks to the stability with warm air
over the cool lake surface. The best chance of seeing any gale force
gusts will again be at the higher observing platforms. Behind the
front, winds will quickly veer from south to NW late tonight. Winds
behind the front are expected to be around 20-25 kts west half and
30 kts east half with some more gale force gusts possible. Could
have extended the Gale Warning to cover the NW wind portion of the
event as well, but decided against it since confidence in seeing
gale force winds behind the front is even a bit lower than it is
ahead of the front. Winds will subside below 20 kts by Tue afternoon
west half, and by late Tuesday night east half, and then remain
light through at least Thursday morning.
On Thursday, a low is expected to lift northward out of the Ohio
Valley and bend back westward towards Lake Huron. Depending on the
track and strength of this low, there could end up being some gale
force gusts on the far eastern lake Thursday into Thursday evening.
However, confidence is still low at this point, so have decided to
just mention that here rather than explicitly include it in the
forecast. Westerly winds around 20 kts are expected across the lake
on Friday followed by lighter winds on Saturday.
Beach Hazards Statement until 9 PM EDT this evening for MIZ014.
Gale Warning until midnight EDT tonight for LSZ264-266.
Gale Warning until 8 AM EDT Tuesday for LMZ248-250.
Gale Warning until 4 AM EDT Tuesday for LMZ221.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
903 PM PDT Mon Sep 20 2021
.SYNOPSIS...The Red Flag Warning previously in effect for the
North and East Bay hills and the East Bay interior valleys has
been allowed to expire as winds have diminished. Tuesday looks to
be even warmer than today, including areas near the water, as
offshore flow continues. Cooling appears in store for Wednesday
as onshore winds and the marine layer return. But that looks to be
short-lived with high pressure and offshore winds returning
Thursday. Dry conditions and mild to seasonably warm temperatures
look to continue through the upcoming weekend.
.DISCUSSION...as of 9:00 PM PDT Monday...Mostly clear skies
prevail districtwide along with quite mild midevening temperatures.
Even around San Francisco Bay, values in the upper 60s to mid 70s
are widespread. Reflecting offshore flow and the diminished solar
heating of the interior as we head into autumn, not a wide range
in high temperatures this afternoon away from the immediate coast.
Downtown San Francisco reached 83, while Livermore was only 5
degrees warmer at 88.
Tuesday looks to be warmer, and based on max temps reached today
plus new 00Z model output and guidance have just made some
significant upward adjustments to the forecast highs, especially
areas closer to the water. Otherwise present forecasts appear on
.DISCUSSION...as of 2:09 PM PDT Monday...Red Flag Warning to
continue through 8 pm this evening. Skies have cleared as offshore
winds have arrived. We are seeing rapid warm-up of temperatures
throughout the region as downslope winds and a drying airmass
produce ideal conditions for some adiabatic warming even though
850 mb temps aren`t too warm. 2 pm temps in the mid 80s will
continue to warm into the upper 80s and lower 90s through 5-6 pm
before slow cooling overnight. Models do show one last burst of
offshore winds across the Napa hills from 03-09z this evening but
not enough coverage or strength to justify an extension of the
warning. Even though winds will become light overnight there will
be little or no humidity recovery thus fire weather conditions
will remain near critical through the overnight hours.
Smoke and haze from the Windy and KNP Complex fires is now
starting to make its way south to north across the Central Coast.
That smoke/haze will continue to push northward into the Bay Area
by sunrise Tuesday morning. This will be impactful for air
quality on Tuesday as we expect temperatures to be even hotter on
Tuesday with some hazy sunshine. The pattern will support rapid
warming of temps under light offshore wind flow and no marine
layer. Similar to today expect temps to quickly warm into the 80s
by lunchtime but then trend even hotter Tuesday afternoon with
widespread temps in the upper 80s and 90s. For locations close to
the coast this will be one of the hottest days so far this
summer/fall. Heat risk will become moderate for sensitive
populations and the smoke/haze likely wont help but the very dry
airmass will allow for nighttime cooling and even getting into
shade will shave several degrees off the hot temps. Even though
there are no Red Flags for Tuesday conditions will continue to be
near critical with the hot temps, low humidity and rapidly drying
fine fuels while the long term drought continues.
By late Tuesday afternoon there are signs of a southerly wind
reversal coming up the coast that should bring cooling as early as
Tuesday late afternoon/evening to the Santa Cruz region, then
those southwest winds should push through the Golden Gate and up
into the North Bay valleys overnight into Weds morning. This
southerly wind reversal will occur as the main ridge weakens and
a shortwave approaches far NorCal on Weds. This will lead to
several degrees of cooling for Weds as onshore winds return with
stratus forecast into SF Bay Weds morning. The amount of cooling
for Weds should be on the order of 5-10 degrees so still warm
inland but not early as hot as Tuesday.
That shortwave then drops into the Great Basin by Thursday. The
circulation around that low, as another ridge of high pressure
builds looks to set up yet another round of offshore winds for the
North and East Bay hills. The forcing for these offshore winds is
slightly different and may not follow the usual diurnal trend we
see of stronger winds at night. Right now expect to see increasing
northeast winds across the Napa hills on Thursday overspreading
the rest of the Bay Area Thursday afternoon and evening. Wind
speeds look moderate but unlike the current event we should go
into that offshore wind with very low humidity values that will
trend as low as 10% by late Thursday afternoon with temps back
into the 90s. The models had been struggling with how the low
would evolve but now seem to be settling on the idea of another
round of offshore winds for Thursday afternoon. Will get through
this current Red Flag but have to quickly reset and see if a fresh
round of Fire Wx Watches will become necessary for the Thursday
Long range remains unseasonably warm and dry into the weekend
with ridging over NorCal.
.AVIATION...as of 04:29 PM PDT Monday...For the 00z TAFs. VFR
conditions through the period as the region remains under the
influence of high pressure and offshore flow. W/NW winds along the
coast this afternoon around 10-15 kt with N/NE winds inland.
Latest HRRR smoke forecast shows increasing total smoke from
wildfires to our SE beginning later this afternoon and progressing
northward overnight tonight. Expect some slant range vis issues
as smoke drifts northward. May also be some surface haze as well
by tomorrow afternoon. Additionally, just at the end of the
current taf period todays local WRF model shows a southerly wind
reversal traveling up the Monterey Coast and moving into the Bay
by tomorrow evening. May or may not see some low clouds into
tomorrow evening, but confidence is low.
Vicinity of KSFO...VFR through the period with increasing smoke
aloft overnight tonight that may create some slant range vis
issues. Onshore winds this afternoon around 15 kt diminishing this
KSFO Bridge Approach...Similar to KSFO.
Monterey Bay...VFR through the period with increasing smoke aloft
from nearby wildfires. The latest HRRR smoke model shows some
increase in near surface smoke as well that may result in haze. As
mentioned above, possible southerly surge tomorrow afternoon that
may or may not bring in some low clouds into Tuesday evening.
W/NW winds this afternoon 10-15 kt diminishing this evening.
.MARINE...as of 08:03 PM PDT Monday...Light to locally moderate winds
will persist through mid week. Northwest winds will then increase
over the outer waters somewhat later this week. Mixed seas
continue with a moderate period northwest swell and southerly
swell. A longer period northwest swell will arrive mid week.
PUBLIC FORECAST: Blier/RWW
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Area Forecast Discussion
National Weather Service Nashville TN
800 PM CDT Mon Sep 20 2021
FOR EVENING DISCUSSION.
A couple of lingering FFW`s will likely be allowed to expire
within the hour. Rainfall has dropped off considerably and the
current warnings are there to account for rain that has already
fallen. At this time, we are awaiting updated forecasts from the
RFC to update our river products. The public forecast appears to
be in good shape with POP`s diminishing as the evening progresses.
The evening sounding from OHX looks much the same as 24 hours ago,
with modest instability and high PWAT. Have already updated the
forecast to expire the Flash Flood Watch. No further updates are
planned at this time.
00Z TAF DISCUSSION.
BNA/MQY/CKV/CSV...Ongoing showers across Middle Tennessee are
starting to decrease in coverage. At this time, it appears that
impact at our terminals during the next couple of hours will be
minimal. The HRRR shows a further decrease in activity during the
early evening, with an overnight lull before convection starts to
increase again during the late morning and afternoon. Have
included VCTS for tomorrow to handle the possibility of daytime
storms. Look for MVFR ceilings to develop later tonight with some
fog possible at CSV.
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
954 PM EDT Mon Sep 20 2021
High pressure will continue to extend across the Mid-Atlantic states
through tonight. The high will drift toward the Appalachians and
result in cold air damming over the western Carolinas and Virginia
Tuesday and Tuesday night, as a warm/wedge front develops
northeastward across the Piedmont. The front will then continue to
retreat north and west across the Mid-Atlantic states Wednesday, in
advance of a strong cold front that will cross the region Wednesday
.NEAR TERM /THROUGH TONIGHT/...
As of 950 PM Monday...
Surface high pressure continues to extend into the area from the
northeast this evening, along with mid/upper level ridging located
along/just off the Mid-Atlantic coast and into the northeast U.S.
This has allowed for a continuation of dry conditions across
central NC, with the moist an unstable atmosphere located just to
our south and west. The is quite evident in the PW gradient across
the Carolinas. The SPC meso analysis page (via the RAP initialization
for 01Z) has PW`s ranging from around 0.8 inches across the north
northeast Piedmont/northern Coastal Plain of central NC to around
2.3 inches across portions of the SC Lowcountry, while the 00Z/21st
KGSO sounding with a PW value of 1.12 inches.
Dry weather will generally continue this evening (with possibly a
brief shower or sprinkles across our far southeastern counties).
However, as the mid/upper level ridge begins to lift off to the
northeast tonight and a deep mid/upper level trough shifting
eastward across the central U.S. we will see moisture surge
northward across the area, first across the western Piedmont during
the early morning hours of Tuesday. The bulk of the heavy rain will
remain to the west overnight as a weak impulse lifts northward in
the increasing southerly mid/upper flow across the western half of
NC. Low temps tonight are generally expected to range from the mid
60s to around 70 degrees.
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 400 PM Monday...
Perturbations and anomalously rich deep-layer moisture (PWATs of 2
to 2.25") in confluent, low/mid-level flow will edge ewd and across
all of cntl NC by late Tue and Tue night.
At the surface, a ridge over the Mid-Atlantic will retreat wwd
toward the Appalachians, while a wedge/warm front develops newd
across the Piedmont of the Carolinas and VA. That front will
separate probable low overcast, periods of light rain/showers, and
temperatures in the lwr 70s over the wrn Piedmont from lwr/mid 80s
and first half of the day dry conditions in the Coastal Plain. In
those 80s along and east of that front, weak instability and CINH
will support subsequent scattered to numerous showers and isolated
storms during the afternoon, all of which will then continue through
the night as the aforementioned moist axis drifts overhead. The GFS
appears to continue to suffer from convective feedback, and to a
lesser degree the NAM, with multi-inch bulls-eyes of QPF over n-cntl
SC and w-cntl NC early Tue. Discounting those wet solutions and
following WPC guidance, basin average rainfall amounts throughout
the forecast period are expected to range from just a couple of
tenths of an inch in the Coastal Plain to three quarters to one inch
over the wrn/srn Piedmont, with swaths of locally higher amounts of
1-3" in briefly training convection and downpours. Lows 65 to 70.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 340 PM Monday...
Wednesday and Thursday: Central NC will be under the influence of
southerly flow, situated between an approaching trough/cold front to
the west and high pressure to the east-northeast on Wednesday. The
southeasterly return flow around the high will pump moist air into
the area from the Atlantic while southwesterly flow ahead of the
front will advect warm moist air in from the Gulf. Aloft, the high
amplitude trough extending NNE/SSW from the Great Lakes to the Deep
South will move eastward toward the East Coast on Wednesday. Most
model guidance has a low closing off over the mid-MS/OH Valley on
Wednesday and possibly being cutoff from the parent trough over that
region as the trough lifts east-northeast through eastern Canada
Wednesday night. The low will drift slowly northward into the Great
Lakes through Thursday, getting picked up by the next northern
stream trough moving eastward through Canada Thursday night/Friday.
At the surface, the cold front extending from the Great lakes,
southwest through the TN Valley and into LA/TX will move eastward
over/though the Appalachians late Wednesday/Wednesday night.
Meanwhile, a surface low along the front over the OH Valley will
quickly deepen as it lifts northward in response to the closing low
aloft. The lows should become stacked over the eastern Great Lakes
or Ontario by Thursday night.
Uncertainty: There are still some significant discrepancies between
the available models with respect to the timing of the front as it
moves through NC Wednesday night/Thursday. The GFS continues to be
the quickest, the EC the slowest, and the NAM in between the two.
The GFS and NAM are also stronger with the high moving in behind the
front. The fropa timing will of course impact rainfall, cloud cover,
and temperatures through Thursday night.
Precipitation: The best chances for rainfall will be on Wednesday
into Wednesday night. Central NC remains in a marginal risk for
excessive rainfall during that time period, but exactly how much and
the duration will depend on when and how quickly the front moves
through (i.e. which model pans out). PWATS should still be greater
than 1.5 inches, but not quite as high as the previous 24 hours.
Regardless, generally expect about an inch of rain or less, though
some locally higher amounts are possible.
Temperatures: Highs on Wednesday could still rise into the upper 70s
to mid 80s and lows possible dropping into the mid 50s NW to mid 60s
SE, but there is a medium-high bust potential on that given the
above concerns. Temperatures Thursday/Thursday night should be
several degrees lower, highs in the mid to upper 70s and lows in the
(possibly) upper 40s NW to upper 50s east.
Friday onward: The cold front should have progressed through central
NC by Friday morning, with cool high pressure centered over the
central Appalachians and a trough along the Carolina coast
persisting through Friday night. A weak trough will move through the
area on Saturday, but should be dry. Aloft, a weak shortwave
traversing the base of the trough over the Appalachians will lift
through the region on Friday. The parent trough will remain over the
mtns as another low moves south out of central Canada and into the
Great Lakes/OH valley over the weekend. Both the low and the parent
trough will slowly move eastward to along the East Coast of the US
through the weekend, possibly lingering into early next week. For
now there is too much uncertainty to get into specifics, but
generally expect this period to be dry with below to near normal
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
As of 830 PM Monday...
24-hour TAF period: VFR conditions will prevail across central NC
through the early overnight hours. However, moist south/southeast
flow off the Atlantic will result in ceilings lowering to MVFR and
IFR by close to daybreak in the western Piedmont (including
INT/GSO). A few LIFR ceilings even can`t be ruled out around
daybreak, with IFR ceilings continuing through much of the day in
the west thanks to cool NE flow and a CAD regime. Visibilities will
also be lowering from MVFR to IFR through the day with periods of
showers. At RDU and FAY, isolated showers will begin around mid-
morning, increasing in coverage by the afternoon, when an isolated
storm or two can`t be ruled out. This area will be east of the cool
surface wedge so ceilings will only lower to MVFR in the morning and
should continue mostly MVFR through the day, though some brief
scattering to VFR is possible at times behind any showers. Even
farther east at RWI, the dry mid-level ridge off the coast will be
close enough to keep conditions VFR through much of tomorrow, with a
chance for showers/storms and MVFR conditions not coming until late
in the afternoon.
Looking beyond 00Z Wednesday: The moist axis will continue to move
eastward to include all of central NC on Tuesday night, then linger
until a cold front and following much drier air sweep across the the
region Wednesday night-Thursday morning. This moist axis will result
in a high probability of LIFR-IFR ceilings by night and IFR-MVFR
ones by day. In addition, a good chance of showers will continue
through Wednesday night, with some isolated storms also possible
Wednesday afternoon/evening. West-to-east clearing and a return to
VFR will result behind the front on Thursday, with a continuation
VFR conditions through at least Saturday.