Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/21/18
Area Forecast Discussion
National Weather Service Wakefield VA
1129 PM EDT Sat Oct 20 2018
A strong cold front moves across the region overnight. Canadian
high pressure builds into and over the area Sunday and into the
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 1130 PM EDT Saturday
Based off latest radar and high res data, added isltd shwrs to
the nrn half of the fa over the next svrl hrs as the boundary
marches se across the area. Could see wind gusts 35-45 mph as
the bndry comes through given the sharp pressure rises behind
Waiting on secondary cold front, currently crossing the
mountains, to move into the western part of the forecast area
between 03-06z, and then move off the coast by around 09z.
Latest guidance suggests a few more showers will cross the
eastern shore as the upper trough swings through overnight. Will
keep slight chance pops in the this area through early morning.
However, the big story for tonight will be the wind potential.
Decent pressure rises around 2-4 mb per hour combined with
strong cold advection with 850mb temps quickly dropping to
around -2C by 09z will allow for gusty NW winds to develop
across the entire forecast area initially with the immediate
post frontal mixing, then continuing with gusty winds close to
the coast due to the continued mixing from the warm Ches
Bay/coastal waters. Forecast soundings from the HRRR and NAM
show impressive mixed layer winds developing across the entire
forecast area. As such, will increase winds and wind gusts
across the entire area later tonight with even inland areas
potentially seeing gusts of 35-45 mph briefly. Close to they
bay, especially the eastern and southern sides, the reduced
friction from the over water fetch combined with a better mixed
layer will yield gusts in the 45-50 mph range. As such, a wind
advisory will be in effect for areas adjacent the Chesapeake
Bay/Atlantic Ocean. In addition, the best pressure rises occur
over the MD eastern shore overnight into Sun morning, and
combined with the mixed layer will also have a wind advisory
over the entire eastern shore.
Lows tonight will drop fairly rapidly behind the front, with areas
west of RIC dropping into the lower 40s. Perhaps a few upper 30s in
the colder areas. With later frontal passage across the east,
will still drop temps back into the middle 40s to lower 50s
close to the coast.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
As of 300 PM EDT Saturday...
Beyond the gusty winds mainly Sunday morning, expect the weather
into Tuesday to be quiet with high pressure in control. With dew
points expected to drop into the upper 20s/lower 30s Sunday night
under the high, it is possible that temperatures at or below
freezing could occur away from the water. The main factor which
would prohibit temps from dropping to below freezing is the expected
warm advection and height rises. In addition, the center of the high
stays over NC, so it is possible that there will be a weak westerly
wind especially just above the surface. As such, will maintain temps
at or above freezing but will not issue a freeze watch for any area
at this time. Otherwise, mostly sunny each day. Highs Sunday in the
low-mid 50s, warming to the mid-upper 60s by Tuesday.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 345 PM EDT Friday...
Much of the week looks dry with below normal temperatures as
the mean trough remains in place and even reinforced across the
eastern part of the country. The Middle Atlantic will stay in
dry west to northwest flow so beyond tonight, the next chance
for rain will be later Friday night into Saturday as the ECMWF
and the GFS suggest some type of southern stream system
developing. Highs Wed-Friday will likely be in the 50s with
850mb temps forecast to be 5 to 8 degrees below normal for this
time of year. Warmer on Saturday, but still below normal with
temps upper 50s/mid 60s.
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
As of 725 PM EDT Saturday...
VFR conditions expected at all terminals during the 00Z TAF
period. There could be an isold -SHRA over the lower MD Eastern
Shore overnight. Gusty NW winds expected later tonight into
Sunday morning at all sites, with widespread 30+ kt gusts, with
ORF/SBY/ECG perhaps seeing 35-40kt. Expect winds to diminish
some Sunday afternoon.
Outlook...VFR conditions with high pressure in control for much
of the coming week.
As of 330 PM EDT Saturday...
A strong cold front crosses the waters tonight bringing with it
a strong surge of CAA late tonight into Sunday morning. Combo
of the CAA surge along with sharp pressure rises results in wind
gusts to 40 kts out of the NW over a majority of the marine
area. Gale Warnings remain in effect for all of the coastal
waters, the Bay, lower James River, and Currituck Sound through
Sunday morning. Strong SCA`s for the other eastern Virginia
rivers for now, but would not be surprised to see a few gusts in
excess of 35 knots for these locations as well. Data suggests a
3-6 hour period of strongest gusts between 09Z-15Z Sun. Waves
(3-5 ft) and seas (5-8 ft) build in response to the gusty
Expect diminishing winds Sunday afternoon and expect the gales
to be replaced with SCA`s at that time. High pressure builds
overhead Sunday night allowing winds to drop below SCA levels.
SSW winds below SCA levels return Mon/Tue as high pressure
builds back over the waters.
MD...Wind Advisory from 5 AM to 11 AM EDT Sunday for MDZ021>025.
NC...Wind Advisory from 5 AM to 11 AM EDT Sunday for NCZ102.
VA...Wind Advisory from 5 AM to 11 AM EDT Sunday for VAZ077-078-086-
MARINE...Gale Warning until 1 PM EDT Sunday for ANZ630>634-638-650-652-
Small Craft Advisory until 4 PM EDT Sunday for ANZ635>637.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1159 PM EDT Sat Oct 20 2018
Cold air advection underway with lake-enhanced moisture resulting in
low end VFR conditions persisting overnight into tomorrow morning.
Strong gusts have mostly subsided, but a few elevated gusts of 15-20
knots will be possible through much of the night. Wind direction
will be out of the northwest overnight. Winds begin to back out of
the west by the morning and eventually out of the southwest by late
afternoon/early evening as a high pressure drifts south of the area.
Some MVFR ceilings will be possible by the morning, but expect
clouds to begin scattering as the surface ridge enters the central
For DTW...Low end VFR ceilings remaining at or below 5,000 feet
through the night with potential MVFR ceilings to develop by morning.
.DTW THRESHOLD PROBABILITIES...
* High for ceilings 5000 ft overnight into tomorrow morning.
Issued at 337 PM EDT Sat Oct 20 2018
Convective showers and isolated-scattered thunderstorms tracking
through southeast Michigan with small hail and gusty winds of 45-60
MPH (see FNT/PTK/ARB/DET obs) this afternoon. Temperatures now
crashing into the 40s, which will help to stabilize the low levels
just enough (to limit thunderstorms), with post upper wave subsidence
kicking in, likely ending shower activity by 00z. Wind advisory will
continue into the early evening hours (along/south of M-59), but
best surge with the cold advection/rise-fall pressure couplet looks
to be across northwest Ohio early this evening.
With the amount of cold air spilling south through the Central Great
Lakes tonight, 850 MB temps lowering to -8 to -9 C, isolated light
snow showers/flurries are not out of the question, even with the
unfavorable northwest trajectory, as RAP does indicate saturation at
850 MB. Even so, the RAP is still indicating little in the way of
activity over southern Lake Huron, while the 12z HIRes-ARW and
latest HRRR seem to be a bit more realistic with multiple bands,
with some modest impact to the eastern shoreline of the Thumb. Will
continue with scattered mention overnight right near the shoreline,
but little or no snow accumulation with surface temps likely holding
in the mid 30s most of the night near the mild waters of Lake Huron.
Quiet weather to end the weekend, as pronounced surface ridge axis
tracks through the Central Great Lakes on Sunday. Warm advection
through the day, but 850 MB temps still not reaching zero by day`s
end. Continued southwest flow on Monday, but 850 MB temps not
budging much as large scale lift from next shortwave trough drops
into the Western Great Lakes, and over the Central Great Lakes
Monday night. It will be breezy again on Tuesday (gusts 30-35 mph),
but amount of cold air spilling in behind this low looks to be less
than current one.
Upper level northwest confluent flow on Wednesday will then allow
expansive high pressure to build into the region, persisting through
the end of the work week, with dry weather and slightly below normal
temps on tap.
Cold air is quickly filtering into the Central Great Lakes late this
afternoon, a quick uptick in northwest winds to Gales should occur
over the majority of the marine waters this evening. Even locations
under small craft advisories will likely briefly touch Gale force.
Rain/Snow Squalls will also be prevalent much of the night, with
winds slowly decreasing as we head into Sunday.
Winds will also back more southwesterly on Sunday and should
remain at or below 25 knots. Another wind shift will occur early
next week with the next cold front, but northwest winds expected to
stay under 30 knots at this time.
MI...Lakeshore Flood Advisory until 6 AM EDT Sunday for MIZ049.
Lake Huron...Gale Warning until 1 AM EDT Sunday for LHZ362-363-441-462>464.
Small Craft Advisory until 4 PM EDT Sunday for LHZ421-442-443.
Small Craft Advisory until 5 AM EDT Sunday for LHZ422.
Lake St Clair...Small Craft Advisory until 4 AM EDT Sunday for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EDT Sunday for LEZ444.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Green Bay WI
1028 PM CDT Sat Oct 20 2018
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Sunday
Issued at 211 PM CDT Sat Oct 20 2018
The latest RAP analysis and satellite/radar imagery show a potent
shortwave trough moving over northeast WI early this afternoon.
Rain and snow showers are ending over east-central WI associated
with this trough. Meanwhile, cloud cover becomes more orientated in
bands behind the trough, and snow showers have become more
confined to the snow belt of north-central WI. Winds have been the
gustiest within the snow showers, with gusts up to 40 to 45 kts
reported at Marshfield to Green Bay. Winds will generally remain
gusty up to 35 kts through the afternoon, though will gradually
subside. Forecast concerns generally revolve around lingering snow
shower chances and winds tonight.
Tonight...As shortwave energy continues to move southeast across
the eastern Great Lakes, a ridge of high pressure will build into
the region from the west. Ample dry air associated with high will
rapidly push east across the area this evening, causing lake
effect cloud bands to retreat north closer to Lake Superior. A few
flurries or light snow showers may linger over northern Vilas
county in the evening. Winds will diminish with nocturnal cooling
setting in, dropping below 20 kts (except near Lake Michigan) by
8-9 pm. Temperatures will not fall too far due to the wind, with
lows ranging from the low 20s at Tomahawk to near 30 degrees along
Sunday...High pressure will quickly advance across the area during
the morning and result in mostly sunny conditions through midday.
During the afternoon, a shortwave trough moving just north of Lake
Superior will push a weak front into northwest WI. Moisture is
extremely limited along the front, but will likely see an increase
of mid-clouds across much of the area. No precip is expected
however. With a strengthening south wind, temps will warm into the
low to mid 40s at most locations.
.LONG TERM...Sunday Night Through Saturday
Issued at 211 PM CDT Sat Oct 20 2018
No major weather impacts expected through the extended portion of
Sunday night through Monday: A weak surface ridge will continue to
slide off to the east of the area Sunday night as a broad surface
and upper-level low pressure system shifts across northern Manitoba
into Ontario. This low will drag a surface trough/weak cold front
across the CWA from west to east late Sunday night into Monday
afternoon. The better moisture and forcing will remain north of the
CWA, main over Lake Superior into portions of the U.P. This will
keep most locations dry, with only a few extra clouds along the
MI/WI border through Monday afternoon. Overnight lows will be in the
mid 20s to low 30s with daytime highs in the upper 40s to low 50s.
Monday night into Tuesday: As the aforementioned trough axis remains
nearby, 850mb temperatures are progged to cool to around -7C to -8C.
This, along with Lake Superior surface temperatures around 6C to 7C
and northwest flow, will lead to lake effect snow potential over
north-central WI. This will be especially true over Vilas County
Monday night through Tuesday. No major system forcing is expected,
so any snow should remain fairly light with inversion
heights/moisture remaining at or below 5 kft. Only a small portion
of the convective cloud layer is expected to reach above the
-10C to -11C isotherm, so snowflake size should remain small and
give low snow to liquid ratios. Outside of some increased cloud
cover along with MI/WI border, the rest of the CWA is expected to
remain dry. Monday night lows will be in the 30s with highs expected
to be in the 40s for Tuesday.
Tuesday night through Wednesday night: High pressure will move
across the area through this time period, both aloft and at the
surface. This will allow for dry conditions, partly cloudy skies and
relatively calm winds. This will allow for some cold temperatures
Tuesday night with ideal radiational cooling conditions. Lowered
temps a few degrees to trend that way. Temperatures will remain well
below normal with overnight lows dropping into the low to mid 20s
northwest to low 30s southeast. Daytime highs will be in the upper
40s to around 50.
Thursday through Friday: Return flow will kick in on the back side
of the departing high pressure system. This will lead to increasing
moisture and cloud cover across much of the CWA ahead of the next
system, likely next weekend. There will also be a steadily
increasing chance of precipitation across the area. At this point, a
consensus of the models is the best way to handle this time period
with some model differences continuing.
.AVIATION...for 06Z TAF Issuance
Issued at 1023 PM CDT Sat Oct 20 2018
As expected, cold north flow across Lake Superior was making it
difficult to clear the clouds out of northeast Wisconsin. But
low-level flow will be veering overnight, so the clouds will
eventually shift east. Once the current low clouds depart, expect
just patches of clouds to stream across at times through
tomorrow, with VFR conditions anticipated.
Area Forecast Discussion
National Weather Service Phoenix AZ
825 PM MST Sat Oct 20 2018
Some occasionally unsettled weather will prevail across the region
through early next week. Mainly slight chances for showers will
exist across southwest and south-central Arizona, especially across
higher terrain areas. Temperatures will also cool slightly with
additional rain chances from Phoenix eastward. Rain chances shift
mainly east of Phoenix Monday into Tuesday. Drier conditions will
move into the region by the middle of next week with temperatures
remaining near seasonal normals.
A large, slow moving closed low with 2 distinct vorticity centers
off the California coast has induced deep southerly flow and modest
moisture advection over the SW Conus this afternoon and evening.
Objective analysis and sampled 00Z KTWC indicate effective MLCape in
a 500-1000 J/kg range, albeit capped by notable warm layer between
650-600mb. Thus far, shallow convection continues to percolate near
the leading ridge of the higher theta-e airmass though hasn`t
breached the capping layer. With better synoptic ascent still
lagging well to the west, HREF members and HRRR output continue to
suggest little more than a few isolated showers through the
overnight. However, there continue to be good agreement that lift
will increase Sunday morning with more pervasive showers from
Phoenix eastward. Thus, have trended POPs towards this scenario.
Otherwise much like the past several nights, increasing east winds
topping a partial decoupled boundary layer will create widely
varying temperatures between foothills and valley locations. Some
adjustments were made to better account for a tighter
wind/temperature magnitude and gradient.
/256 PM MST Sat Oct 20 2018/
The upper level low will slowly shift eastward through the middle
of the week. Multiple disturbances and shortwaves will move
around the trough tonight through Monday which will serve as a
better lifting mechanism for showers and storms. This combined
with continued moisture advection along a southeast to northwest
corridor oriented through Tucson and to just west of Phoenix
should eventually allow for some isolated showers and possibly a
few thunderstorms late this evening. The HREF has continued to be
really optimistic about this the past day, showing increased
showers along the aforementioned corridor initiating around 12Z.
Activity than slowly shifts to the east through the remainder of
the day tomorrow.
Mid-level winds will also begin to shift more out of the south
and even out of the southwest across southwest Arizona starting
Sunday morning. This will bring drier air into south-central
Arizona starting Sunday afternoon while shifting the bulk of the
shower or thunderstorm activity mainly east of Phoenix. The upper
low will also become temporarily more stationary later Sunday
while a stronger jet enters the base of the trough. This will keep
rain chances focused mainly east of Phoenix for Monday into
Tuesday with best chances early Monday night due to a brief
increase in dynamics aloft. Temperatures Sunday and Monday will
edge downward a bit from today, or closer to seasonal normals.
Finally the upper level low is forecast to open up and shift to
the northeast of the region later on Tuesday, but broad scale
troughing should still remain over the region through Wednesday.
This will keep temperatures stable before a gradual warming trend
commences starting Thursday. Models are still showing a strong
ridge eventually shifting eastward off the Pacific into the
Southwestern U.S. as early as Friday, but there are some model
timing differences. Either way it seems likely we will see more
significant drying and temperatures a few degrees above normals
going into next weekend.
South-Central Arizona including KPHX, KIWA, and KSDL:
Winds and scattered showers will be the two primary aviation impacts
through Sunday evening across the Phoenix terminals. Models continue
to suggest scattered showers developing later Sunday morning and
persisting into the afternoon from central Phoenix eastward. An
embedded isold TS could be possible but unlikely while cigs remain
7K ft or higher.
Breezy east winds will persist through the overnight hours as the
low levels will have difficulty decoupling and forming the typical
morning inversion. As such despite 35-40kt east winds near 2K ft,
the shear may not be as abrupt within a LLWS context. However, have
continued the LLWS mention into Sunday morning given the heightened
speeds versus more typical conditions.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation impacts will exist through Sunday evening under mostly
clear skies. SFc winds will favor a northerly component through the
night, but become light and variable during the day Sunday as the
pressure gradient relaxes through SE California.
Aviation Discussion not updated for amended TAFs.
Tuesday through Saturday:
Low pressure over the region will keep wetting rain chances
elevated during the Mon-Tue timeframe across south-central
Arizona. The best chances for rain continue to be over the high
terrain north and east of Phoenix. There is also a potential for
isolated thunderstorms as well on Monday. Dry conditions and
slightly lower humidities should return during the Wed-Fri period
as winds aloft become more westerly. Winds should remain at 15-
20mph or less area-wide. Minimum humidities in the 25-50 percent
range Mon (lowest over SE CA) will fall into the 20-40 percent
range (lowest over SE CA) by Thursday.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
Area Forecast Discussion
National Weather Service Las Vegas NV
849 PM PDT Sat Oct 20 2018
Updated to the forecast this evening to account for the expected
development of showers and isolated thunderstorms tonight. This
included just a few minor adjustment to coverage and intensity of
precipitation. The short-range CAM guidance has been remarkable
consistent with the development of showers and isolated
thunderstorms overnight. The HRRR brings this activity up from
the south near Phoenix as it pushed across the Las Vegas area and
heads northward tward tomorrow morning. The new run of the
SPC/SSEO also shows a similar set up. All this seems legit given
the forcing from the upper low moving inland from the Pacific. The
afternoon sounding here at Vegas indicated an eroding cap at
around 600mb which is likely the primary inhibition for activity
thus far. What does this all mean? Basically, we expect that
activity will begin to develop shortly for southern, central and
eastern portions of our CWA. Things appear on track thus far.
.PREV DISCUSSION... /issued at 115 PM PDT Sat Oct 20 2018/
.SYNOPSIS...Increasing shower and thunderstorm activity is expected
tonight across mainly southern Nevada and Northwest Arizona as a low
pressure system approaches the area. Residual activity will linger
into Sunday before drier and more stable air pushes in Monday.
Improving conditions are expected next week with dry conditions and
a warming trend on the way.
.SHORT TERM...through Monday night.
While conditions across the region remain dry at this hour, change
is already underway with moisture advection on the increase.
Afternoon visible satellite imagery depicts cloud streets across the
Mojave desert and an increasing cumulus field across eastern Mohave
county. MDCRS samples from aircraft in the region suggest a
moderate capping inversion remains in place this afternoon around
600mb, which will continue to limit the vertical extent of cloud
development until later this evening when mid-level cooling begins
to increase as stronger ascent moves in. As such, I kept PoPs fairly
low through 8pm tonight, and then began ramping them up as shower
and thunderstorm activity increases across Mohave county and lifts
northwest into Clark and southern Lincoln counties. It looks like
best window for the Las Vegas Valley will be between 11pm and 6 am
for shower activity, through recent model trends suggest the most
favored area tonight may be across the eastern half of Clark county.
The main threats from shower and storm activity tonight will be
brief heavy rain and associated wet and slick roadways. Some minor
flooding is possible, but swift northward motion should limit that
risk for most areas unless more persistent banding features develop.
Fairly strong deep layer shear will also promote the potential for
some small hail with the stronger thunderstorm cores.
On Sunday, the main focus areas of precipitation will lift into
Lincoln county in the morning, but additional shower and storm
activity will likely break out in the afternoon thanks to cool
temperatures aloft and surface heating of a fairly moisture rich
boundary layer. Brief heavy rain and small hail will again be
Drier conditions will move in Monday as the trough pushes inland. A
few terrain driven showers will remain possible across Lincoln and
Mohave counties, but should be isolated to scattered at best.
.LONG TERM...Tuesday through Saturday.
High pressure ridge will build in during the long term period, with
heights risings dramatically Thursday into Friday as the high builds
over the southwest. This will lead to an extended dry period with
temperatures climbing above normal. Nudged temperatures upward, but
they may still be a tad on the cool side given the strength of the
.AVIATION...For McCarran...Winds will remain north-northeast for
much of the day with speeds 7-9 kts. By late afternoon, winds will
become light and variable lasting through the overnight hours and
into Sunday. Clouds will continue to increase today around 8 kft. By
6Z tonight, showers will pop up in the vicinity of the terminal and
last through Sunday afternoon.
For the rest of southern Nevada, northwest Arizona and southeast
California...Gusty north winds are expected along the Colorado River
Valley, particularly at the KIFP TAF site, with gusts up to 25-30
kts possible. Elsewhere, winds will be light through the forecast
period. Clouds will continue to increase through the day today.
Showers will be in the vicinity of the terminals around 6Z at all
sites but KBIH. Higher terrain will be obscured at times.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
SHORT TERM/LONG TERM...Outler
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