Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/16/18
Area Forecast Discussion
National Weather Service Charleston SC
1023 PM EDT Mon Oct 15 2018
.SYNOPSIS...
Summer-like pattern with above normal temperatures will prevail
until a cold front crosses the region Wednesday into Wednesday
night. Cooler high pressure will then move in through late week
before a stronger cold front likely pushes through Saturday
night.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
As of 1015 PM: KCLX detected a few weak showers drifting east
over the central Savannah River Valley. The latest run of the
HRRR indicates that the showers will slowly fade as they track
east. Sfc observations and satellite indicates that no fog has
developed across the forecast area so far this evening. However,
give dewpoint depressions and latest MOS, I would expected at
least isolated fog to develop by midnight.
As of 735 PM: The going forecast appears on track.
As of 625 PM: Weak coastal showers have generally dissipated
along the southern SC coast. KCLX indicates a well defined sea
breeze from Bulloch north to Allendale County, advancing inland.
The dewpoints in the wake of the sea breeze should increase into
the low to mid 70s tonight. Given the rising dewpoints, thinning
cloud cover, and light winds, fog should begin to develop late
this evening. Fog late tonight may become locally dense.
Previous Discussion:
Isolated showers extending from the Tybee Island/Hilton Head
area north along the I-95 corridor to start will dissipate by
early evening. Then, low-level flow veering toward the SW
overnight should hold additional isolated/scattered showers
over coastal waters and just offshore of coastal counties.
Overnight, the combination of elevated dewpoints, light surface
winds and relatively dry air aloft should combine to support
fog/stratus. The latest forecast indicates patchy fog
developing around midnight then expanding to areas of fog late
tonight/toward daybreak Tuesday. Fog could become locally dense.
However, W/SW winds increasing to 15-20 knots just off the
surface later tonight could promote sufficient mixing to prevent
a widespread/dense fog event. Also of note, the latest forecast
holds significant fog just off the immediate coast. However,
low-level winds could push inland fog/stratus toward the coast
late. Will continue to assess tonight. Otherwise, unseasonably
warm temps will only bottom out around 70F inland and in the mid
70s at the coast.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
After some morning fog Tuesday we expect unseasonably warm
temperatures into Wednesday ahead of an approaching cold front which
should push through from northwest to southeast Wednesday into
Wednesday night. A few showers and thunderstorms are expected
Tuesday/Tuesday night, mainly inland, then across most of the
forecast area Wednesday into Wednesday night as the front pushes
through. Not much rainfall is expected overall and the chance of
severe storms is very low. Much cooler and drier conditions are then
expected Thursday, although can`t completely rule out a few showers
near the central GA coast where some moisture convergence is likely
due to the increased northeast winds.
Temperatures will remain above normal through Wednesday for most if
not all of the forecast area, with the northwest tier toward the Pee
Dee/Midlands/CSRA the only area that could see below normal temps
depending on the frontal passage timing and associated rain/cloud
coverage. Below normal temperatures on likely Thursday with highs
only ranging from near 70 close to the Pee Dee/Midlands to mid 70s
generally south of I-16.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
By Friday, the center of surface high pressure is expected to shift
offshore as another low pressure system moves east near northern
Ontario with an associated cold front draped across portions of the
northern U.S. Model guidance continues to show this front moving
with purpose, crossing the Appalachians by Saturday and moving
through the forecast area by Sunday morning. Other than southernmost
zones where better moisture persists, a dry forecast will be
advertised heading into the weekend, with precipitation chances
increasing Saturday and Sunday with the front.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
KCLX indicates a well defined sea breeze from Bulloch north to
Allendale County, advancing inland. The dewpoints in the wake of
the sea breeze should increase into the low to mid 70s tonight.
Given the rising dewpoints, thinning cloud cover, and light
winds, fog should begin to develop at the terminals late this
evening. The TAFs will continue to feature MVFR vis for fog
between 8Z-13Z.
Extended Aviation Outlook: VFR will prevail through Saturday at
KCHS/KSAV. Brief ceiling/vsby restrictions possible from morning low
clouds/fog. Some showers and/or weak thunderstorms also possible,
mainly during the afternoon Tue and again Wed/Wed night.
&&
.MARINE...
Tonight: S/SE winds around 10 kt will turn toward the S/SW
later tonight. Seas will remain 2-3 ft.
Tuesday through Saturday: A cold front will move through the waters
Wed/Wed night from north to south with increasing winds/waves after
that, likely reaching Advisory levels for all waters into Thu
night/early Fri. Conditions could go back downhill Saturday as a
cold front approaches and possibly moves into the waters later in
the day.
&&
.CLIMATE...
Record high maximum and record high minimum temperatures will be
challenged until midweek. We have listed records that fall within
2-3 degrees of forecast values.
Date Location Record High Record High Minimum
Mon 10/15 CHS 87 (1985- already tied)
CXM - 75 (1925)
Tue 10/16 CHS 87 (1942) 71 (1985)
CXM 87 (1925) 73 (1933)
SAV 90 (1941) -
Wed 10/17 CHS - 70 (1999)
SAV 91 (1921) -
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...NED/SPR
SHORT TERM...RJB
LONG TERM...
AVIATION...NED/RJB
MARINE...RJB/SPR
CLIMATE...
Area Forecast Discussion
National Weather Service Dodge City KS
623 PM CDT Mon Oct 15 2018
...Updated aviation discussion...
.SHORT TERM...(This evening through Tuesday)
Issued at 1215 PM CDT Mon Oct 15 2018
Despite a persistent strong southwest flow aloft, dry conditions
will continue through Tuesday afternoon as a prevailing west to
northwest downslope flow near the surface reinforces a much drier
air mass across western Kansas. Near to below freezing temperatures
are expected tonight even as the aforementioned west to northwest
downslope flow draws slightly warmer air at H85 into the region.
The question will be whether temperatures drop low enough to
warrant a Hard Freeze Warning for those areas failing to drop
below 29F this morning, specifically zones along the Oklahoma
border and portions of south central Kansas. Under mostly clear
skies, the HRRR and HiResW-ARW suggest lows generally down into
the upper 20s(F) to the lower 30s(F) overnight regardless of
downslope westerlies. However, fairly light winds and the clear
skies may allow for lower temperatures in lower lying areas. Will
have to keep possible headlines in mind later this afternoon for
any hard freeze potential late tonight for the areas mentioned
above. A modest warming trend will continue into Tuesday with
highs well up into the mid/upper 50s(F) to the lower 60s(F).
.LONG TERM...(Tuesday night through Monday)
Issued at 100 PM CDT Mon Oct 15 2018
Precip chances remain absent across western Kansas Wednesday as
surface high pressure is slow to push eastward, only giving way to a
southeasterly upslope flow by Wednesday night. Chances pick up a
little Thursday as a closed upper low in the deep Desert Southwest
begins to lift northeast into the Four Corners Region creating an
increasingly difluent and strengthening southwest flow aloft across
the Western High Plains. Meanwhile, a prevailing southeasterly
upslope flow will slowly draw low level moisture back into central
and much of southwest Kansas, but will do very little to increase
instability. Still, enough lift will be present to support the
potential for possible light rain development across portions of
southwest and central Kansas with minimal rainfall amounts expected.
Otherwise, the drier pattern resumes through the weekend as yet
another frontal boundary is projected to push through western Kansas
Friday bringing another shot of dry air into the Western High Plains.
Temperatures are expected to remain a little below normal Wednesday
as a broad surface high is slow to shift eastward across the Central
Plains, allowing for little erosion of the cooler air mass across
the high plains. Should see highs only up into the mid/upper 50s(F)
again Wednesday afternoon with a few lower 60s(F) possible further
southeast. Similar highs are expected Thursday before a weak cold
front pushing through Friday helps keep high temperatures near to
below seasonal through the early part of the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 622 PM CDT Mon Oct 15 2018
Weak high pressure aloft along with high pressure at the surface
will keep skies clear and winds light and variable through this
period.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 28 60 37 61 / 0 0 0 0
GCK 27 58 33 58 / 0 0 0 0
EHA 33 58 37 56 / 0 0 0 0
LBL 28 60 37 59 / 0 0 0 0
HYS 25 60 37 59 / 0 0 0 0
P28 28 62 40 63 / 0 0 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
Hard Freeze Warning from 1 AM to 9 AM CDT Tuesday for KSZ080-081-
087>090.
&&
$$
SHORT TERM...JJohnson
LONG TERM...JJohnson
AVIATION...Gerard
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
921 PM CDT Mon Oct 15 2018
.UPDATE...
While the ongoing forecast is in good shape minor tweaks were made
to the QPF, PoP, and weather grids to reflect ongoing radar trends
and to align the forecast with what the high resolution models show
for the rest of the night.
A flash flood situation has developed across the Hill Country
through the evening as 1 to 3 inches of rain have fallen over the
last 6 hours, bringing the daily total across much of Llano,
Gillespie, and parts of Burnet county up to 5 to 6 inches. While this
rain has fallen over several hours the ground is so saturated from
recent rains that anything that falls is turning into runoff
resulting in Flash Flooding across these areas. Reports from county
EMs and sheriffs offices in Llano and Gillespie county show that
multiple roads are closed across both counties due to water over the
roadways. This include roads that typically do not flood or are not
considered low water crossings. The message tonight across the Hill
Country is that if you don`t have to get out and travel, stay home.
Flooded roadways at night are difficult to detect, and with such
widespread flooding and multiple roads closed being out and about
across these areas tonight is dangerous.
Over the next several hours the HRRR, Texas Tech WRF, and other high
resolution models show rainfall moderate rain continuing to move
northeast over the Edwards Plateau and Hill Country before lifting
northward out of the area Tuesday morning. Because of the saturated
soils this has become less about intense rainfall rates, and more
about longer duration rains resulting in runoff and flooding. Flash
and River Flooding will continue to be a possibility through the
night from Edwards through Kerr, Gillespie, up to Llano and Burnet
Counties. Area rivers have also responded to the rainfall with parts
of the Nueces, Guadalupe, and Llano Rivers all above flood stage
tonight.
To those along and east of I-35 isolated to scattered light rain will
be possible through the overnight hours with lows dropping into the
mid to upper 40s.
&&
.PREV DISCUSSION... /ISSUED 714 PM CDT Mon Oct 15 2018/
AVIATION...
Periods of SHRA are expected at the terminals through at least 14-18Z
Tuesday as an upper level speed maxima overrides a frontal boundary
located around 850 MB draped north of the terminals. This will result
in visibilities dropping as low as LIFR in heavier SHRA, with
IFR/MVFR conditions prevailing as ceilings remain trapped beneath a
low level frontal inversion. With the surface pressure gradient
relaxing, expect northerly winds to begin decreasing but remain
generally elevated in the 10-15 knot range. Amendments are expected
to handle more intense SHRA that approach the terminals.
PREV DISCUSSION... /ISSUED 410 PM CDT Mon Oct 15 2018/
SHORT TERM (Tonight through Tuesday Night)...
Much cooler temperatures along with widespread rain and a few
thunderstorms can be found across south central Texas this afternoon.
Temperatures are currently in the upper 30s to upper 40s across the
region, compared to 24 hours ago when temperatures were mainly in the
80s to lower 90s.
Widespread rain along with a few embedded thunderstorms are expected
to continue through tonight as southerly warm air advection above
the cold low-level northerly flow continues. For the early part of
this evening, the main concern is expected to remain out west along
the Rio Grande, where the HRRR suggests some stronger convection from
Mexico will move northward into the Rio Grande plains. For the
overnight hours, the models suggest additional showers and embedded
thunderstorms will continue, with the heavier totals expected to
remain across the Rio Grande plains, southern Edwards Plateau and
Hill Country. Locally heavy rainfall may also spill over into Tuesday
and with this in mind, we have opted to extend the Flash Flood Watch
into early Tuesday evening. Storm total amounts through Tuesday of 1
to 3 inches with a few totals of 4 to 6 inches are expected.
LONG TERM (Wednesday through Monday)...
We could see a brief break in the rainfall on Wednesday for areas
along and east of I-35. However, west of I-35, rain chances continue
to remain high as additional shortwave energy moves out of Mexico
into the Rio Grande plains. Rain chances look to increase again on
Thursday as the medium range models show a series of disturbances
moving up from deep south Texas into the region. The forecast for the
upcoming weekend into early next week remains uncertain as the
operational GFS and ECMWF diverge on the mid-level flow pattern. The
GFS suggests a drier forecast with a surge of cool and dry air on
Saturday. The ECMWF also shows this surge of cooler air, but
maintains a warm air advection pattern and keeps much higher rain
chances intact. For now, we will keep rain chances in the forecast,
but have gone a little lower than the ECMWF.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 46 44 47 45 54 / 100 90 80 50 40
Austin Bergstrom Intl Airport 47 46 47 43 55 / 100 90 80 50 40
New Braunfels Muni Airport 48 45 49 45 56 / 100 90 70 40 30
Burnet Muni Airport 43 41 44 43 53 / 100 100 80 60 50
Del Rio Intl Airport 47 43 48 46 54 / 70 90 70 70 70
Georgetown Muni Airport 45 43 46 45 53 / 100 90 80 50 40
Hondo Muni Airport 50 44 50 48 57 / 100 90 70 50 40
San Marcos Muni Airport 46 44 48 46 55 / 100 90 70 40 30
La Grange - Fayette Regional 51 47 50 49 58 / 80 80 60 30 30
San Antonio Intl Airport 48 45 49 46 57 / 100 90 70 40 40
Stinson Muni Airport 53 47 52 48 58 / 100 90 70 40 30
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Tuesday evening for Bandera-Blanco-Burnet-
Edwards-Gillespie-Kendall-Kerr-Kinney-Llano-Maverick-Medina-Real-
Uvalde-Val Verde-Zavala.
&&
$$
Aviation...Huffman
Short-Term/Long-Term...Treadway
Area Forecast Discussion
National Weather Service Marquette MI
756 PM EDT Mon Oct 15 2018
.SHORT TERM...(This evening through Tuesday)
Issued at 357 PM EDT MON OCT 15 2018
Water vapor imagery and RAP analysis show a vigorous shortwave
moving across the Upper Lakes. Wave gave a nice boost to shsn across
the area this morning into the mid aftn as it moved across the area.
Another month or so down the road, and this type of system would
have produced hvy lake enhanced snow. Now, with subsidence spreading
over the area behind the shortwave and with the negative impact of a
still relatively high fall sun angle, -shsn have diminished to
isold/sct coverage over the w despite 850mb temps around -9C.
Diminishing trend has also taken hold over the e recently.
Otherwise, it`s been another chilly day under mostly cloudy skies.
Temps are mostly in the 30s. Upstream, next shortwave of interest is
already diving se thru Saskatchewan/Manitoba.
The next shortwave will dive se into the Upper Lakes by Tue morning.
In response to this wave, waa will begin with low-level winds
backing to the sw tonight. This will bring an end to ongoing light
lake effect pcpn from w to e this evening. With a decent shot of
isentropic ascent noted on the 290k sfc (roughly 700-750mb), might
be able to generate a little -sn over the nw tonight, and then late
tonight over the e where low-level winds may back just enough to
help bring some shallow moisture off Lake MI. Cold front will then
sweep across the area during the day Tue. CAA is not especially
strong with 850mb temps dropping from around -2C in the morning to
-5 to -7C by 00z. With water temps roughly -6 to 8C, conditions will
be marginal for lake effect pcpn, especially with the negative
effect of daytime heating. Cyclonic flow will be helpful, but
overall not expecting anything more than isold/sct coverage of lake
effect showers, not too different from what is currently occurring.
Will be a blustery day with winds gusting 20-30mph... up to 35mph or
so on the Keweenaw. Expect high temps in the upper 30s in the higher
terrain nw to the mid 40s s central and e.
.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM EDT MON OCT 15 2018
Upper air pattern consists of a 500 mb closed low over the desert sw
and a deep trough across the eastern half of the U.S. with a ridge
in the sern U.S. and in the Pacific NW 00z Wed. Upper air pattern
changes little 00z Fri except that the ridge in the sern U.S.
retrogrades a bit to the Gulf Coast. Typical northwest wind flow
lake effect pcpn pops will continue through Wed night, then Thu
looks dry and temperatures get to near normal. Did not make too many
changes to the going forecast overall.
In the extended, the GFS and ECMWF show a 500 mb trough in the
northern plains and central Rockies down into the desert sw with a
ridge over the wrn U.S. 12z Fri. A cold front will be moving through
the area on Fri with 850 mb temperatures dropping down to -6C to -9C
over Lake Superior 12z Sat as a deep 500 mb trough moves into the
upper Great Lakes. This trough moves off into the lower Great Lakes
12z Sun. A shortwave ridge moves into the Rockies 12z Mon with a
deep and broad trough across ern N.A. and another shortwave moving
into the upper Great Lakes on Mon. Temperatures look to stay below
normal for this forecast period and will have lake effect pcpn for
most of this forecast period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 730 PM EDT MON OCT 15 2018
Although there is a break in the cloud cover this evening at the
terminals, more clouds are on the way. This next batch should keep
ceilings in the VFR category overnight, but could easily teeter
into MVFR, especially closer toward daybreak. Additionally, some
more showers could develop overnight into tomorrow, with KCMX
having the higher chances of seeing a temporary reduction in
ceilings and visbys tonight. Look for more lake effect/enhanced
shower activity at all three terminals during the day tomorrow.
Winds currently out of the W-SW will initially become more
southwesterly this evening before veering westerly. These westerly
winds will be breezy/gusty during the day tomorrow.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 357 PM EDT MON OCT 15 2018
Typical fall pattern will affect Lake Superior during this week with
windy conditions dominating. A few periods of gales are expected.
There will be some w to nw gale force gusts over eastern Lake
Superior this evening, but a more solid period of gales will develop
over western Lake Superior tonight under strengthening sw winds
ahead of the next disturbance dropping toward the Upper Lakes. As
winds veer w to nw on Tue, gales will transition to eastern Lake
Superior though some gale gusts may continue over portions of
western Lake Superior. Winds of 20-30kt will then generally prevail
Tue night/Wed. A brief period of lighter winds will follow Wed night
as a high pres ridge passes. Next period of gales will arrive Thu
aftn/night as another disturbance drops toward the Upper Lakes.
Winds will mostly be in the 20-30kt range Fri/Sat, but not out of
the question that a period of gales will occur at least over eastern
Lake Superior during this time.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
Gale Warning from 2 PM Tuesday to midnight EDT Tuesday night for
LSZ265>267.
Gale Warning from 11 PM EDT /10 PM CDT/ this evening to 8 AM EDT
/7 AM CDT/ Tuesday for LSZ162-263-264.
Lake Michigan...
None.
&&
$$
SHORT TERM...Rolfson
LONG TERM...07
AVIATION...lg
MARINE...Rolfson
Area Forecast Discussion
National Weather Service Paducah KY
857 PM CDT Mon Oct 15 2018
.UPDATE...
Issued at 856 PM CDT Mon Oct 15 2018
With a mid-evening update, will keep the current coverage and
timing of the Frost Advisory in place for parts of southern
Illinois, and adjacent parts of southeast Missouri and southwest
Indiana tonight.
However, a minor vort center (possibly a weak baroclinic leaf) has
set up over extreme eastern Oklahoma this evening. This would
support a greater probability of broken to overcast cloud cover
over the WFO PAH forecast area through at least 6-8z (1 to 3 am
CDT).
After that time, some thinning/breaks should take place to reduce
the opaque sky cover in and around the frost advisory area. The
effective time for lowered cloud coverage to aid frost development
may be only 1-3 hours. Cold air advection has been more efficient
this afternoon and this evening, so had to adjust temperatures and
dewpoints downward 1-2 degrees. This will place the vulnerable
areas in the Frost Advisory closer to reaching critical
temperature/radiational cooling levels despite a short residence
time of clearing skies between midnight and daybreak Tuesday.
So, no changes to the Frost Advisory. Main sensible weather
changes made were to increase opaque cloud cover, reduce
temperatures and dewpoints overnight.
&&
UPDATE Issued at 620 PM CDT Mon Oct 15 2018
Revised aviation discussion for 00Z TAFs.
&&
.SHORT TERM...(Tonight through Wednesday night)
Issued at 154 PM CDT Mon Oct 15 2018
All the short term discussion is temperatures and the impact of,
ie Frost and headlines thereof. Problematic is the slow clearing
and light gradient that will be maintained, and there may be high
clouds advecting overtop the cleared out areas. But the consensus
build is that for northern reaches, where temps will drop into the
lower to middle 30s, there will be enough of a clear out late,
with temps low enough (low to mid 30s), to call for headline
Frost across our northern tier counties...namely along and north
of the Interstate 64 corridor generally.
Clouds/pcpn will linger longer than model indications, although
the HRRR keeps picking up on this, carrying into the evening, for
our southeast counties.
As surface High pressure slides east with time, then we`ll see a
better clear out/cool temps with light winds as the surface High
over over the Ohio valley Wed night... which may well result in
another headline.
.LONG TERM...(Thursday through Monday)
Issued at 154 PM CDT Mon Oct 15 2018
By 12Z Thursday, the center of surface high pressure will be
situated over northern portions of our area. Temperatures during the
early morning hours will likely bottom out in the mid to upper 30s.
With the clear and mainly calm conditions, along with those
temperatures, we will likely see some frost formation, especially
across southern IL, southwest IN and parts of west KY. Throughout
the day on Thursday, the high will be slowly shifting east. However,
our area will remain dry with highs in the mid to upper 50s.
Clouds will be increasing from the west as the flow becomes
southwesterly Thursday night into Friday, and advects moisture
northeast ahead of an advancing cold front. The GFS insists that
rain could start as early as 06Z Friday out in far western portions
of the cwa. Timing and QPF between the suite of model data continues
to be problematic. However, it still appears as though Friday into
Friday night will be the best time frame for rain to fall. Placement
of higher PoPs for each 6 hour period is what remains in question at
this time. However, the GFS ensemble mean QPF is more similar to the
latest ECMWF runs than it is the operational GFS. Therefore, the
operational GFS may be a bit too fast bringing the rain across the
area early Friday.
Despite the model differences early on, most are in agreement on the
departure of the rain. A weak cold front will push through the area
late Friday night. We should see the rain ending during the evening
hours on Friday.
Surface high pressure will build into the area for Saturday
resulting in some breezy conditions early in the day, slackening off
later, with highs a few degrees either side of 60. Patchy frost will
once again be possible late Saturday night into Sunday with lows in
the upper 30s. The rest of the weekend even into Monday looks dry
with below normal highs continuing (mid to upper 50s) along with
most frost probable late Sunday night into Monday morning.
&&
.AVIATION...
Issued at 620 PM CDT Mon Oct 15 2018
Drier air will advect into the region tonight on light north to
northwest winds as high pressure over the Plains takes control.
As a result, MVFR ceilings will continue to clear from northwest
to southeast through the evening, leaving behind VFR conditions
during the remainder of the forecast period.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory from 1 AM to 8 AM CDT Tuesday for ILZ075>078-
080>084.
MO...Frost Advisory from 1 AM to 8 AM CDT Tuesday for MOZ076.
IN...Frost Advisory from 1 AM to 8 AM CDT Tuesday for INZ081-082-
085>087.
KY...None.
&&
$$
UPDATE...Smith
AVIATION...RyanP
Area Forecast Discussion
National Weather Service Mount Holly NJ
936 PM EDT Mon Oct 15 2018
.SYNOPSIS...
A cold front extended from southwestern Quebec, across the
upper Ohio River Valley to the lower Mississippi River Valley
this afternoon. The boundary will progress to the southeast and
it should pass through our region tonight. Another cold front
approaching from the northwest is forecast to arrive on
Wednesday. High pressure is expected to build across our region
from the west on Thursday and Friday, followed by a cold front
late on Saturday.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
930 pm update: Made some minor edits to temperatures and edited
PoPs/Wx grids a little bit more to match radar trends. Forecast
thinking below remains unchanged at this point.
830 pm mesoscale update: I updated the PoPs/Wx grids substantially
based on the past two hours of radar trends. It is becoming
increasingly clear that a predecessor vort max has moved through
the northern Mid-Atlantic, and the cold front is now upstream
of it. When analyzing radar data over the past three hours, the
narrow band of showers along the front quickly fizzled after the
passage of the vort max (and attendant showers, generated from
the midlevels). I suspect weak/transient subsidence upstream of
the vort max combined with the nearly-nonexistent low-level
parcel buoyancy has (have) countered the lift generated by the
front. This process will likely continue until the next
perturbation reaches near/downstream of the front, and as the
23z HRRR suggests, this may not happen until the front is near
or even off the coast of New Jersey.
With the above in mind, greatly reduced PoPs this evening but
did keep them elevated near/east of the Delaware River 02z
onward (though somewhat lower than before). Also narrowed the
region at risk of lightning to the proximity of the front hour-
by-hour. Overall, though, think the risk of gusty showers/storms
along the front is lowering away from the coast and from
Delmarva.
700 pm mesoscale update: Front is quickly approaching the area
and will enter the northwestern CWA in the next hour or two. So
far, the strongly-forced showers along the front have not fared
well, losing some organization and intensity in the past hour or
so. However, as the front moves past the higher terrain of
central PA, it will begin to approach a modestly more favorable
environment to initiate and sustain stronger lift/updrafts.
Slab-like lift along the boundary is expected to resume the
strongly-forced narrow band of showers with increasing chances
of thunder as the front approaches the coast. Hi-res models
showing this process occurring between 02z and 04z generally
near and east of the I-95 corridor. The chances for stronger
convection increase closer to the coast, and with such strong
winds aloft, even low-topped convection with little or no
lightning will be capable of mixing down these stronger winds,
potentially producing gusts strong enough for sporadic wind
damage.
The main questions are if the above processes occur and when.
Hi-res models have been insistent on this occurring, but have
performed rather poorly with the predecessor (downstream) rain
generated from higher levels (likely associated with a weak vort
max). Per the 18Z NAM, the stronger vort max will be moving in
from the southwest between 00z and 03z and is quite evident on
moisture-channel imagery moving through the central Appalachians
at this time. The contributions from large-scale lift in
advance of this perturbation should aid in convective
regeneration, so confidence is fairly high on the "if" question.
The "when" question is more uncertain, and timing is everything
given the speed of the front. If the timing of the vort max is
slow even by an hour, chances are quite low of any substantive
convection developing north of the Mason-Dixon Line before the
front moves offshore. They remain higher in Delmarva given the
northeast-southwest orientation of the front. But, per the
HRRR/NAM Nest, the timing seems to favor development near or
just east of the I-95 corridor between 02z and 03z. We shall
see.
Previous discussion...
A strong upper-level trough will slide eastward from the Great
Lakes and across Ontario and Quebec Canada through tonight. This
will drive a deepening surface low eastward as it tracks well
to our north. An associated surface cold front however will
sweep across our area later tonight. Some showers will move
across parts of the area into this evening well ahead of the
cold front. These should be on the lighter side with the rain
falling mostly from a mid level cloud deck.
As this feature slides eastward an increase in the wind fields
are forecast. The 500 mb flow is forecast to increase to 70-95
knots tonight as the core of an intense mid level jet streak
tracks across much of New York State. As the flow, initially
southwesterly, increases and transports warmer and more humid
air northward, some instability is forecast to develop through
the evening into the overnight hours. The forecast soundings
vary to some degree on the amount of destabilization ahead of
the cold front, however generally up to 500 J/KG may be
realized. The setup looks to be of a high shear/low CAPE one,
and with the strong wind fields coupled with a band of enhanced
ascent near the cold front may result in a narrow band of forced
low-topped convection. Some of the guidance including the high-
res does show a line of showers organizing eastward across our
area by later this evening. There is a narrow line forming in
western Pennsylvania this afternoon and this should be the
feature to watch. It is not all that clear how much lightning
will be generated given the low instability forecast, however if
the line is organized enough locally strong to damaging winds
could occur briefly as the line moves through given the amount
of wind above the surface. This potentially looks to be after 8
PM overall for the area from west to east and is then over with
by 2 AM. This line may become better organized from about the
I-95 corridor on eastward.
The combination of the strong wind field and then the cold air
advection in the wake of the cold front should result in a
period of gusty winds associated with the wind shift. The gusty
northwest winds are expected to diminish by daybreak as the
strongest winds shift offshore and the pressure gradient lessens
some. Temperatures may actually increase some through the
evening as the flow strengthens and the low-level warm air
advection occurs, then temperatures drop off with and following
the showers and cold frontal passage. The dew points will also
tumble overnight in the wake of the cold front. Low temperatures
are mainly a model/continuity blend.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The flow aloft is forecast to be more zonal on Tuesday in the
wake of a strong upper-level trough early on that exits northern
New England. High pressure at the surface centered in the Ohio
Valley is forecast to gradually extend into our area, and this
will loosen the pressure gradient. A northwesterly breeze will
turn west or west- southwest during the afternoon.
As the cold front settles south and east of our area in the
morning, it may tend to stall to our south given the flow aloft
becoming more parallel to it. Some lingering showers are
possible across the far southern areas early, then given dry air
advection within the northwest flow should allow for a dry day.
The cloud cover should clear out quickly from north to south to
start the day, however mid to high level clouds may linger
longer mainly from the Philadelphia metro area on southward.
It will be a cool day with temperatures mainly in the 50s,
however dew points are forecast to drop into the 30s for much of
the area. The high temperatures are mostly a blend of guidance
and continuity.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
We should be well into a typical autumn weather pattern from
Tuesday night through Monday with the polar jet remaining over
the Great Lakes and the Northeast for much of the period.
A mid level short wave trough and its associated surface cold
front are expected to affect our region on Wednesday. The system
should bring limited moisture with it. As a result, we will
mention only a slight chance of afternoon showers across the
Poconos and far northern New Jersey.
Ridging at the surface and aloft are forecast to result in dry
and mostly sunny conditions for Thursday and Friday.
Another mid level trough is anticipated for the weekend. It
should bring a cold front through our region late on Saturday.
We will keep a chance of showers in the forecast for Friday
night and Saturday in the lift ahead of the system.
Dry weather is expected to return for Sunday and Monday.
Below normal temperatures are forecast through the period. The
chill will be most noticeable on the days following the cold
fronts.
Temperatures are expected to drop into the 30s in much of our
region on Wednesday night and Thursday night. A northwest wind
at 5 to 10 mph may preclude the development of much frost on
Wednesday night. However, the wind should become light and
variable on Thursday night and there may be widespread frost in
much of our area, away from urban locations and the immediate
coast.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
This evening...Front will move through between 00z and 05z
across the terminals, likely with showers and a quick switch to
west-northwest winds at RDG/ABE around 01z-02z. Timing looks to
be 02z to 04z near the Philly terminals, and there is a slight
chance of lightning by this point. Confidence is too low for TAF
inclusion here. At MIV/ACY, timing looks to be 03z to 05z, and
the line of showers is expected to intensify to the point where
mention of TS in the TAFs is needed. The main terminal impact
will be the quick switch in wind direction, and it will be
likely accompanied by gusts (perhaps to 30+ kts near the showers
themselves). After frontal passage, any (brief) MVFR conditions
will become VFR quickly as winds become 270-320 degrees with
speeds 10-20 kts and higher gusts. Moderate confidence.
Overnight...Winds become more northwesterly with time and should
diminish to around 10 kts by daybreak. VFR. High confidence.
Tuesday...VFR with northwest winds around 10 kts becoming more
westerly during the mid to late afternoon. High confidence.
OUTLOOK...
Tuesday night...Mainly VFR. Southwest to west wind 8 knots or
less.
Wednesday...Mainly VFR. West to northwest wind 10 to 15 knots.
Wednesday night...Mainly VFR. Northwest wind 5 to 10 knots.
Thursday...Mainly VFR. Northwest wind around 10 knots.
Thursday night...Mainly VFR. Variable wind 6 knots or less.
Friday...Mainly VFR. Southwest wind around 10 knots.
Friday night...Mainly VFR. A chance of showers. Southwest wind
5 to 10 knots.
Saturday...Mainly VFR. A chance of showers. Southwest to west
10 to 15 knots.
&&
.MARINE...
A cold front will cross the area later tonight. Strong winds
above the surface will result in gusty southwest winds ahead of
the front, with peak gusts in the 25-30 knot range. Along and
behind the front, a period of gale force northwesterly gusts are
anticipated for much of the area. As a result, the Gale Warning
continues for tonight. A Small Craft Advisory however continues
for the Upper Delaware Bay. A narrow band of heavier showers
and perhaps some embedded thunder may produce brief stronger
winds later this evening into the overnight.
For Tuesday, a Small Craft Advisory should be needed for the
morning following the Gale as winds and seas subside through the
day.
OUTLOOK...
Tuesday night...Westerly wind gusts may approach 25 knots on
our ocean waters north of Atlantic City.
Wednesday and Wednesday night...West to northwest gale force
wind gusts are expected.
Thursday...Northwest wind gusts of 25 to 30 knots are expected.
Thursday night and Friday...No marine headlines are
anticipated.
Friday night and Saturday...Southwest wind gusts around 25
knots are possible.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 6 AM EDT Tuesday for ANZ431-450>455.
Small Craft Advisory until 6 AM EDT Tuesday for ANZ430.
&&
$$
Synopsis...Iovino
Near Term...CMS
Short Term...Gorse
Long Term...Iovino
Aviation...CMS/Iovino
Marine...Gorse/Iovino