Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/19/21

Area Forecast Discussion

National Weather Service Amarillo TX

 629 PM CDT Sun Apr 18 2021

.AVIATION...
VFR conditions expected throughout the 00Z TAF period. Skies will
remain mostly clear throughout the TAF period with sct high
clouds moving into KGUY towards end of the TAF period ahead of
approaching cold front. Winds will be predominately out of the
southwest at 10-20 kts with higher gusts at times. Near the end of
the TAF period, winds at KGUY will back to more easterly ahead of
approaching cold front.

Meccariello

&&

.PREV DISCUSSION... /Issued 253 PM CDT Sun Apr 18 2021/

SHORT TERM...Tonight through Tomorrow Night...

Latest WV imagery reveals our next upper level trough digging
south out of western and central Canada. This system has a decent
amount of moisture with it based on the expansive area of cool
cloud tops moving southeast through portions of MT and ND.
However, the latest guidance keeps the bulk of this moisture north
of the Panhandles as the much drier system currently over AZ
moves up ahead of the Canadian system, keeping most of its dynamic
influence in the central plains (although the southern jet streak
will clip our northern zones Monday night). At the surface, a
very cold airmass is making its move south into MT and ND at this
time. Sub freezing conditions were noted across southern Alberta
and Saskatchewan. This air will be entering our northern zones as
early as tomorrow evening, and should be clearing our southern
zones by 09z Tuesday (if not earlier). Given the strong CAA and
large density difference that will be associated with this cold
front, it will likely be faster than what most guidance suggest.
Have utilized the HRRR output for timing which was a few hours
faster than the lower resolution models. Wind speeds are also
going to be a concern behind the front Monday night given pressure
rises on the order of 3 to 4 mb/hr (strongest on the Caprock).
The GFS and CMC also indicate a strong 850mb jet of 40 to near 50
knots just behind the front. These 850mb winds will be capable of
mixing to the surface for an hour or two behind the front given
how strong the cold air advection is expected to be. Thus
sustained winds of 30 to 40 mph will be possible, along with wind
gusts near 50 to 60 mph. Wind headlines for Monday night will
probably be needed in upcoming shifts.

As for winter precipitation, accumulations are looking less and
less. This is mostly due to the fact that the best lift and
moisture is progged to stay to our north. Some 700mb
frontogenesis does moves through the area, but it is transient and
doesn`t have much moisture to work with. Forecast soundings hint
at potential for some brief and very light freezing drizzle (if
the dry air right off the surface can be overcome) due to
saturation of supercooled air in the lowest 100mb or so. This
saturated low level air may get cold enough (-8 to -10 deg C) for
some light snow flurries mainly after 06z as far south as
Amarillo. This could be enhanced some by the Canadian River
Effect given the strong north winds. The far northern zones may
see a brief period of saturated DGZs, but there is also a pocket
of dry mid level air showing up in the NAM soundings that won`t be
good for snow accumulations. The GFS is still on board with up to
0.5" of snow in portions of the northern OK Panhandle, as it does
not show the pocket of dry mid level air. Either way, it looks
like impacts will be more from cold and windy conditions than
winter precip, and any accumulations would be mainly limited to
the far northern zones. Can`t rule out some light icing on wind
shields and elevated surfaces with any brief freezing drizzle, but
not expecting impacts to travel.

Speaking of cold, temperatures will certainly fall below freezing
across most of the area before sunrise Tuesday morning. As a
matter of fact, our current forecast brings Amarillo down below
freezing by 06z Tuesday. Will continue the Freeze Watch and expand
it to include all zones. Combine mid 20s to low 30s temperatures
with strong north winds and we end up with wind chill values in
the teens and even some single digits.

Ward

LONG TERM...Tuesday through Saturday night...

Large upper level troughing pattern continues through Tuesday
morning, then starts to break down with slight H2 height rises
going into Thursday evening allowing for temperatures to warm.
Thursday night into Friday an H5 positively tilted trough will
approach the FA bringing slight chance for precipitation in the
far eastern FA. Friday night another surface cold front will move
in from the north as the mid to upper level shortwave axis
traverses the Panhandles. A mid to upper level ridge will build in
Saturday night into Sunday as the trough exits the region
possibly bringing well above normal temperatures out past the
extended period.

One key topic for Tuesday will be the well below freezing
temperatures to start out the day on Tuesday. This combined with
strong northerly winds behind a front around 20 to 25 mph will
keep daytime temperatures held back well below normal Tuesday
afternoon. The winds and gusts will gradually decrease going into
the late afternoon as the pressure gradient relaxes both at the
surface and H85. Daytime temperatures are looking to only reach
the upper 40s to lower 50s. This will be around 20 degrees below
normal. Light winds and clear skies Tuesday night may lead to
below freezing temperatures across the majority of the area
Wednesday morning as well.

For Wednesday, temperatures will only be slightly warmer with
daytime highs in the upper 50s to lower 60s. Even though cloud
cover will increase early Wednesday winds will pick up out of the
south to help warm to these temperatures. Overnight Wednesday into
Thursday most of the area should remain in the mid 30s or just
above freezing with the exception of the for northwest FA.
Thursday a LLTR will build in over New Mexico with its eastern
edge over the far western CWA. This will cause H85 temperatures to
be 10C degrees warmer over the western Panhandles than the
eastern Panhandles. Also, an surface trough will build into the
west bringing drier air. This will cause daytime temperatures to
warm into the mid 60s in the far western FA and only mid to upper
50s in the eastern FA regardless of clear skies and southerly
winds. By Friday the LLTR will propagate east encompassing more of
the FA and bringing daytime temperatures into the upper 60s to
70s.

Friday is also when the next mid to upper level shortwave troughs
moves in from the west. Chances for precipitation with this next
system look to be limited to the far eastern Panhandles into
western Oklahoma. There are some differences in the models at this
time, as the GFS is showing a more westward extent for PoPs. This
is due to a dryline type feature forming as the gradient steepens
from dewpoints in the 20s to 30s west of this boundary and 40 to
50 dewpoints east of the boundary. The previous 06Z run of the GFS
had this feature much more of a true dryline with a triple point
in the north central FA. The new 00Z GFS has a good axis of
theta-e advection at H7 over the eastern two stacks of counties in
the Texas Panhandle. The EC and Canadian have this axis further
east impacting more of western Oklahoma. Have stuck with the NBM
PoPs for now until there is further agreement between the models.
Even if the GFS is right, there will be much cooler H85
temperatures on the moist side of the pseudo dryline. This will
most likely create an inversion at H7 capping off any surface
based convection limiting severe storms.

The cold front of the pseudo triple point will move through
sometime in the afternoon into evening Friday. According to the
NBM, temperatures on Saturday could return to the low 70s as
winds quickly return to an east-southeast direction. The GFS does
show northerly winds all day on Saturday. If this were to be the
case, daytime temperatures on Saturday could end up being cooler.
But overall it looks like a warming trend could be occurring into
the weekend bringing well above normal temperatures in the 80s out
past day 7.

Hoffeditz

&&

.AMA Watches/Warnings/Advisories...
TX...Freeze Watch from late Monday night through Tuesday morning for
     the following zones: Armstrong...Carson...Collingsworth...
     Dallam...Deaf Smith...Donley...Gray...Hansford...Hartley...
     Hemphill...Hutchinson...Lipscomb...Moore...Ochiltree...
     Oldham...Palo Duro Canyon...Potter...Randall...Roberts...
     Sherman...Wheeler.

OK...Freeze Watch from late Monday night through Tuesday morning for
     the following zones: Beaver...Cimarron...Texas.


&&

$$

29/15




Area Forecast Discussion

National Weather Service Newport/Morehead City NC

 1008 PM EDT Sun Apr 18 2021

.SYNOPSIS...
A weak area of low pressure will move past the area on Monday.
A strong cold front moves through the area late Wednesday. High
pressure will build in from the west Thursday and Friday. Next
storm system will arrive in the region by next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 10 PM Sunday...A few isolated showers near the central
Outer Banks and offshore and will continue isolated PoPs for
these areas overnight, but otherwise a dry night across eastern
NC. Skies have cleared and some patchy fog may be able to form,
although will need to watch advancing cirrus shield from the
southwest to see what impact that might have on early morning
fog. No other major changes made to overnight forecast, and will
hold on to partly cloudy skies with overnight lows in the low
to mid 50s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
As of 330 PM Sun...Good amount of PVA aloft in congruence with
low-level convergence as weak low lifts north will support a
more widespread area of precipitation tomorrow morning into the
afternoon, and maintained chance to likely PoPs in the forecast.
Main question for tomorrow is the possibility of any stronger
storms, with limiting factor being moisture availability. PWATs
are likely to remain at an inch or less but a brief period of
southerly return flow could briefly boost surface Tds enough to
build some instability across the area. Both RAP and NAM 3k
soundings suggest CAPEs of 600-800 J/kg as well as effective
shear of 35-40 kt. The threat appears very isolated but a more
robust storm could produce some gusty winds. A few rumbles of
thunder appear probable tomorrow and kept TS mention in the
forecast. Threat will be largely offshore by end of the period
as shortwave energy races eastward and surface front follows
suit, bringing drier air with it.

Low-level thicknesses change little from today and maintained
highs in the low to mid 70s, mid to upper 60s OBX.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
As of 333 AM Sun...A cold front will remain stalled to the
south through the middle of next week, with weak areas of low
pressure moving along it. A strong front will push through the
area Wednesday afternoon, with much cooler air behind it. A
potentially strong low pressure area will approach by next
weekend.

Tuesday...Mainly dry as transitory high slides through ahead of
next deep shortwave trough digging through the ctrl plains
states. Temps near climo in the 70s for highs.

Tuesday night through Wednesday...Area will be under influence
of strengthening return flow Tue night and esp Wed, as stronger
front is progged to push through by late in the day. 18/00z
guidance in better agreement with respect to timing, pushing the
front offshore by early Wed evening. Increased pops a bit from
previous forecast, but global model suite still in disagreement
on how much moisture return is available for thunderstorm
development. Latest ECM is a bit wetter, and therefore bumped up
pops a bit, esp nrn half, where 30-50% pops fcst. Modest
instability and strong shear (50+ kt bulk shear) in place, so if
any storms can organize, a severe threat may be in play.

Wednesday night through Saturday...Much cooler and drier
airmass expected behind the front with high pressure building in
from the W and upper troughing. We could have some Frost/Freeze
concerns, mainly inland zones. Coldest night now looks to be Thu
night/Fri morning as center of high pres will be closer to ENC.
EC/GFS mos guidance show lows falling into the low to mid 30s.
Have not gone quite as cold as guid yet as some light wind may
be in place along with some cirrus potential. Highs Thu
and Fri generally in the 60s with dewpoints falling into the
30s. Temps rebound back to near climo Fri and Sat as air mass
moderates. 18/00Z global models all have a potential strong
storm system or cold front impacting the area by late Sat into
Sun, and have inc pops to high chc. Naturally, timing issues
abound in this long range in time, so will not advertise any
likelies yet.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Short Term /through 00Z Tue/...
As of 720 PM Sunday...VFR conditions expected through the
evening into overnight hours. Scattered high-based cumulus
should mostly dissipate with loss of heating, but some higher
cirrus may move in from the southwest through the late night
hours. Given the potential for some clearing near the TAF sites,
and an easterly onshore flow, plus signals in the numerical
guidance, did introduce a period of MVFR fog (5 miles) toward
morning at the TAF sites. Any fog should quickly dissipate after
daybreak Monday. Scattered TSRA coverage expected tomorrow
with approach of upper level system and surface cold front.
Localized areas of sub-VFR conditions are possible in heavier
activity.

Long Term /Monday night through Thursday/...
As of 333 AM Sun...Pred VFR conditions expected through the
period. Mainly dry Tue, then another chc of showers or storms
Wed as a strong cold front approaches.

&&

.MARINE...
Short Term /Tonight and Monday/...
As of 10 PM Sunday...Not much change to conditions at late
evening with E/NE winds 5-10 knots with a few higher gusts over
the northern tier. Seas are around 2 feet with 10-11 second wave
periods. Conditions expected to remain quiet overnight as weak
low pressure meanders north towards the waters, with winds
falling to around 5 kt or less by daybreak Monday.

Conditions expected to change pretty quickly tomorrow as low
lifts northward and cold front races towards the waters. SW flow
expected to increase to 10-15 kt by the afternoon across
southern waters with weaker easterly to northeasterly flow
elsewhere before front crosses early evening. Guidance differs
on intensity of surge behind the boundary and favored a somewhat
stronger solution, favoring northerly winds at 15-20 kt. A few
gusts to 25 kt are possible for outer central waters but window
of impacts too small to warrant any headlines. Seas build to 3-4
feet, particularly for central waters, in response to the surge.

Long Term /Monday night through Thursday/...
As of 333 AM Sun...Have used a heavier blend of the NBM, as
NWPS too low on seas through Tue. A strong cold front will
approach the waters Wednesday, pushing through Wednesday
afternoon and early evening. SCA conditions likely to develop
Wed afternoon with gusty SW flow ahead of the front, then
stronger NW winds 20-30 kt and seas 4-7 ft developing behind it.
Conditions improve with diminishing winds and seas by Thu.

&&

.MHX WATCHES/WARNINGS/ADVISORIES...
NC...None.
MARINE...None.

&&

$$

SYNOPSIS...MHX
NEAR TERM...CTC
SHORT TERM...MS
LONG TERM...TL
AVIATION...CTC/TL/MS
MARINE...CTC/TL/MS



Area Forecast Discussion

National Weather Service Twin Cities/Chanhassen MN

 654 PM CDT Sun Apr 18 2021

.UPDATE...
Issued at 637 PM CDT Sun Apr 18 2021

Updated to include 00z aviation discussion below.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 253 PM CDT Sun Apr 18 2021

The key messages of the short term forecast center around the strong
cold front that will through the region this evening. Temperatures
are in the 60s ahead of the front with southwest winds and mostly
sunny skies, but temperatures are in the 30s behind the front with
northerly winds and cloudy skies. An area of rain/snow showers is
ongoing just behind the front.

Today and Tonight - No significant changes to the forecast, as the
timing of the frontal passage remains fairly consistent. Did trend
back the pops a bit slower since they are lagging the surface front.
The precipitation is quite intense, and that is leading to cooling
and snow across northwest Minnesota. For us, we`ll be warmer to
start, and the precipitation should focus more across Lake Superior,
so we shouldn`t see the intensity and therefore expect mainly rain
showers. This could mix in with snow across southern Minnesota later
tonight, but no accumulation is expected.

Monday and Monday Night - Cold air advection will continue for
Monday and that will keep temperatures in the 40s for highs. In fact
some locations north of I-94 could stay in the upper 30s. Winds will
be brisk, out of the northwest around 15 mph with gusts near 20 mph.
This type of set up usually yields some rain/snow showers, but the
post-frontal air mass is so dry that the forecast soundings only show
a shallow layer of clouds. The HRRR does have showers mainly east of
I-35 during peak heating, so did add some sprinkles across western
WI. These will quickly dissipate after sunset, and then expect
clearing skies with lows in the 20s across the region. It is too
early in the growing season for any frost/freeze headlines, but this
certainly looks like a hard-freeze with several hours below 30
degrees.

.LONG TERM...(Tuesday through Sunday)
Issued at 253 PM CDT Sun Apr 18 2021

A trough moving across Minnesota will start off the long term period
on Tuesday. Our temperatures will remain cool with highs only in the
40s, but overall we should remain dry as this feature will not have
much moisture to work with. The highest chance for precip will remain
to our south. This reinforced shot of cooler air will stick around
through Wednesday, however, it should be at least a few degrees
warmer than Tuesday thanks to clearing skies. Ridging moves in by
Thursday, allowing temperatures to return to seasonable normals in
the upper 50s and low 60s.

The forecast is a bit less certain heading into Friday through the
remainder of the period, but it appears that this will be our window
for our next chance for precip. Guidance depicts a shortwave moving
across Iowa Friday, leading to a chance of showers across central and
southern Minnesota and western Wisconsin. Inconsistencies exist with
the timing and strength of a cold front late Friday into Saturday,
so have opted to leave the NBM as is until there is a better
consensus.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 637 PM CDT Sun Apr 18 2021

NE-SW oriented cold front currently pushing southeast through
southern MN and western WI. Strong contrast in temps and winds seen
with the front; colder with strong N to NW winds behind the front
while ahead of the front features warmer temperatures with breezy S
to SW winds. All sites will shift to NW shortly after initialization
with winds nearing 20G30kt for a couple hours before settling back to
15-20G25-30kt. All sites will have a brief bout of -SHRA, likely not
lasting more than an hour or so, followed by several hours of MVFR
ceilings. The duration of the MVFR ceilings will be longer in eastern
MN through western WI. Meanwhile, western and southern MN will break
out to VFR ceilings overnight through most of Monday, with sky cover
scattering out by Monday evening.

KMSP...Strong winds upwards of 40kt have since settled down just
before initialization, thus making winds more commonly 15-20kt with
gusts 25-30kt likely through this evening before diminishing slightly
for the remainder of the TAF period. A few showers are possible in
the first hour or so, then dry thereafter. Ceilings likely to drop to
between 2-3 kft later this evening into the early morning hours then
VFR thereafter.

/OUTLOOK FOR KMSP/
Tue...VFR. Wind NW 10 kts.
Wed...VFR. Wind NW 10G25 kts.
Thu...VFR. Wind SW 10G20 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&

$$

UPDATE...JPC
SHORT TERM...JRB
LONG TERM...Dye
AVIATION...JPC




Area Forecast Discussion

National Weather Service Marquette MI

 804 PM EDT Sun Apr 18 2021

.SHORT TERM...(This evening through Monday)
Issued at 437 PM EDT SUN APR 18 2021

The short term will bring another return back to winter. Water vapor
imagery and RAP analysis show a shortwave trof extending from Hudson
Bay to ND. Associated sfc cold front runs from James Bay across ne
MN to SD. Shra are occurring along/just behind front with shra
switching to shsn within about 3hrs of fropa. Closer to home, it`s
been a warm/dry day and generally partly to mostly sunny skies.
Temps in the interior are in the mid 50s to around 60F. Lake breezes
are keeping lakeside locations cool in the low/mid 40s. With dwpts
as low as the upper teens/lwr 20s F, RH has fallen to 20-30pct in
the interior.

Approaching shortwave will amplify as it swings se across the Upper
Great Lakes. Much of the model guidance indicates a weakly closed
mid-level low will form over the fcst area with the center passing
across northern Lake Superior. With 12hr 500mb height falls around
100m tonight and a nice upper diffluence signature within left exit
of upper jet surging into the western Great Lakes, stage should be
set for a band of shra mixing with/changing to shsn moving across
the fcst area tonight. Of concern is the lower level cyclonic flow
that develops under postfrontal caa regime dropping 850mb temps
around -11C and the amplifying trof/falling heights. Further aided
by brisk upsloping NW winds, expect an upslope/lake enhanced snow
scenario to develop overnight into Mon morning. High terrain of the
w and nw fcst area will be favored for this event. DGZ ends up
mostly above the best upward motion so SLRs will be on the low side,
probably around 10 to 1. 12hr snow amounts over the high terrain
from around KIWD ne up the spine of the Keweenaw overnight/Mon
morning may push low SLR winter wx advy criteria of 3 or more
inches. For now, given the greatest amounts pinned locally to the
high terrain, will issue an SPS for the western counties to
highlight the potential of hazardous travel conditions due to some
roads likely becoming slushy/snow covered, at least in spots, for
the Mon morning commute. Winds will also ramp up behind the front as
sfc low pres wave develops on the front over Lake Superior and
briefly deepens. Wind gusts of 25-35mph should be common, developing
nw late tonight then spreading across the area thru Mon morning.
Gusts up to around 45mph are expected at lakeside locations exposed
to a nw wind from the Keweenaw eastward.

So, a blustery, much colder day is on the way for Mon. During the
day, expect temps generally in the upper 20s/lwr 30s F across the w
and n. Temps may sneak up to 40F across the s central, but given the
expectation of abundant cloud cover, that may be optimistic. Loss of
deeper moisture/relaxing cyclonic curvature of the low-level winds
will lead to diminishing snow over the w and nw fcst area during the
aftn. To the e, conditions for lake enhanced snow never become
nearly as favorable as over the w. Minor snow accumulations under 1
inch are expected. Limited daytime heating and moisture off the lake
may support some development of isold -shsn/flurries well inland
during the day.

.LONG TERM...(Monday night through Sunday)
Issued at 327 PM EDT SUN APR 18 2021

A active early long term period with the tail end of a lake effect
snow event followed by a quiet period thanks to a 1027mb surface
high shifting southeastward into the northern Plains. Expecting
below normal temps initially before warming up Thursday and Friday,
with a weekend finish near normal following the passage of a cold
front this weekend.

Starting off Monday night, lingering troughing over the region with
the mid-level low just east of our forecast area will help maintain
the unseasonable colder temperatures. Overnight 850mb temps are
progged to remain about -12 to -14 over the region under
northwesterly flow off Lake Superior. With Lake Superior hovering
near +3C resulting in a delta T of 15 to 18, lake effect snow
showers are expected across the northwest wind snow belts. While
there is decent lift through the DGZ, model soundings show an
inverted V at the lower levels, indicating any snow will have to
overcome the dry air near the surface. If earlier showers are able
to erode the dry layer some, that could add to the snow
accumulations. Generally, expecting an inch or two being possible,
mainly across the Hurons and in the northwest wind belts east of
Marquette. The northern half of the Keweenaw could also see another
half inch or so on top of their daytime accumulations. Overnight
lows are expected to bottom out in the low 20s, but if cloud cover
breaks away from the lakeshores, particularly in the interior west,
some mid to high teens can`t be ruled out.

As the upstream high pressure sinks into southern Saskatchewan
Tuesday, anticyclonic flow and increased subsidence should bring an
end to any early lake effect snow showers. With temps hovering
around -10C during the day Tuesday, expecting day time highs to
remain largely in the 30s. Some low 40s across the south-central
can`t be ruled out. A weak shortwave is expected to migrate south
through the region late Tuesday night into Wednesday. This
enhancement may help develop some flurries or light snow showers,
but with drier low levels, notable accumulations are not expected.
Daytime highs in the upper 30s across the north half and near 40
south half are expected.

Height rises resulting from the upstream high building southeastward
into the central and eastern Plains should help clear out the skies
Wednesday night. With the colder air aloft lingering, winds becoming
light and PWATS near 0.25", expecting an opportunity for some good
radiational cooling. Lows right now look to be in the low 20s with
mid teens in the colder interior west, but I wouldn`t be surprised if
guidance trends colder, especially in the interior central and east.
With the ridge persisting over the region Thursday and Friday,
sunshine and WAA will help temps rebound back into the 50s. The next
precip chances look to be Friday night or Saturday, but there are
noticeable timing differences among the 12z guidance. The GFS looks
to be the fastest solution with the cold front moving into the
region Friday night. This contrasts well with the slower Canadian
and Euro solutions, whom delay the system until Saturday afternoon
or evening. Given there is still plenty of time for things to change
and for the guidance to reach a better consensus, ran with NBM pops
for now.
&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 757 PM EDT SUN APR 18 2021

A cold front will move through the area tonight. Expect a period
of -shra changing to -shsn as the front passes. Expect these
snow showers to continue into Mon morning, especially at
KIWD/KCMX. With the pcpn, expect conditions at all terminals to
fall to at least MVFR. Upsloping postfrontal winds at KIWD/KCMX
may result in IFR conditions at times, especially at KIWD.
Postfrontal nw winds will also be gusty to 20-30kt, strongest at
KCMX and KSAW where some gusts to 30-35kt appear likely.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 437 PM EDT SUN APR 18 2021

Strong cold front will sweep across Lake Superior tonight. Along the
front, a low pres wave will also develop and briefly deepen. Thus,
after fropa, nw winds will ramp up, especially from central to
eastern Lake Superior overnight thru Mon. Increasingly colder air
and 3-4mb/3hr pres rises on the backside of the low pres wave will
further boost winds. Thus, expect high end nw gales of 40-45kt to
develop from central into eastern Lake Superior overnight thru Mon
morning. Not out of the question that there could be an hr or two
where wind gusts reach storm force in a corridor from n of the
Keweenaw Peninsula se toward Grand Marais. Winds will diminish from
w to e Mon aftn thru Mon night. While winds will fall blo 20kt over
the w by sunrise Tue, winds may still be gusting to around 25kt over
the e. Winds generally blo 20kt are then expected thru the midweek
period.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Lakeshore Flood Advisory from 8 AM to 4 PM EDT Monday for MIZ001.

  Lakeshore Flood Advisory from noon to 10 PM EDT Monday for
     MIZ006-007.

Lake Superior...
  Gale Warning from 8 AM to 11 PM EDT Monday for LSZ251-267.

  Gale Warning from 5 AM to 11 PM EDT Monday for LSZ249-250-266.

  Gale Warning from 5 AM to 8 PM EDT Monday for LSZ265.

  Gale Warning from 2 AM to 8 PM EDT Monday for LSZ244-245-264.

  Gale Warning from 2 AM to 2 PM EDT Monday for LSZ243-263.

  Gale Warning from 8 AM to 8 PM EDT Monday for LSZ248.

Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...JP
AVIATION...Voss
MARINE...Rolfson




Area Forecast Discussion

National Weather Service Paducah KY

 1037 PM CDT Sun Apr 18 2021

.UPDATE...
Issued at 1035 PM CDT Sun Apr 18 2021

Aviation update.

&&

.SHORT TERM...(Tonight through Monday night)
Issued at 245 PM CDT Sun Apr 18 2021

Scattered showers will continue to develop and move east across
our region the rest of the afternoon into this evening just ahead
of an upper level trof. Both the HRRR and RAP show CAPE values of
200-400 J/kg across our region and surface LIs of 0 to -2, with
instability quickly diminishing after 00z. We have had a couple of
lightning flashes so far, so we will keep isolated thunderstorms
in the the forecast through 00z. Loss of heating and the
progression eastward of the upper trof will gradually diminish the
shower activity from west to east between 00z-05z.  Another
cooler than normal night can be expected tonight with lows in the
39-44 degree range.

Dry conditions will return overnight as a surface high moves over
east Texas by 12z Monday. The high will become centered over the
Gulf Coast states by 00z Tuesday. We will see mostly sunny to
sunny skies on Monday, and with winds becoming southwest, high
temperatures will reach near seasonable readings in the upper 60s
to near 70 degrees. Lows Monday night will be a couple of degrees
warmer than tonight, though still just a little below normal.

.LONG TERM...(Tuesday through Sunday)
Issued at 245 PM CDT Sun Apr 18 2021

The main story beyond Monday continues to be colder temperatures and
possible record lows, the chances for frost and/or freeze and even
maybe the possibility of frozen precip for some locations.

The main culprit of these potential weather elements is a upper
level system that will be located over eastern parts of Canada and
down into the upper Midwest and northern Plains states. An shortwave
embedded in this system will pivot down across the central Plains
states during the day on Tuesday. This system will be reaching the
far northern and western sections by Tuesday afternoon, so cloud
cover will likely keep highs on the lower to mid 60s in these
locations, while further east, upper 60s to near 70 degrees should
be attainable.

A cold front associated with this upper level wave will be making
its way across the area during the day on Tuesday. The deeper
moisture and associated precipitation is mostly post frontal, so the
best chances for precip will be in the far western reaches of the
CWA Tuesday afternoon, spreading east across the rest of the area on
Tuesday evening. While there are differences in the GFS/ECMWF
ensembles with regards to exact timing of the precipitation, the
latest NBM looks reasonable for now, continuing with the idea that
the latest deterministic GFS may be too fast. While there may be
some lingering QPF in the far east after 06Z Wednesday, most of the
area should be dry for that time frame.

We continue to look closely at temperatures as they rapidly fall
with the passage of the cold front Tuesday afternoon through Tuesday
night. The chances of ice nucleation in the dendritic growth zone
will be limited and short lived, but not non existent. The mid level
moisture needed for nucleation sure does not stick around long but
deep low level moisture is slower to move out. Therefore, still
going with the idea that while we could see a brief changeover or
mix to snow Tuesday evening/overnight, it is not expected to last
long.

Frost does not look as likely on Wednesday morning due to a fairly
good pressure gradient in place, as the center of the surface high
will still be to our southwest. If scattered frost does occur, it
would be most likely in our western sections where the wind will be
the lightest. However, temperatures near or below the freezing mark
are highly likely especially in the far western and northern
sections of the area. Latest GFS/ECMWF ensembles agree with this
idea. The latest NAEFS also agree on these highly anomalous
temperatures showing some deviations well below normal. The main
issue is, how long will we remain at freezing or below. Latest
consensus is that we should near the freezing mark toward sunrise,
but it will be brief. Will let future shifts decide on freeze
headlines maybe for our far west/north. In addition, record lows
Wednesday morning could be tied or broken.

Despite the cold start on Wednesday, highs will reach into the low
to mid 50s across most of the area, as sunshine and strong mid April
sun should help to warm things up. The only fly in the ointment is
there are some signals of another shortwave rotating down across the
area on Wednesday, which may bring more cloudiness. The GFS and many
of its ensemble members hint at some minor QPF as this occurs.

Better chances of frost will prevail across most of the area on
Thursday morning, as the gradient loosens. Temperatures are forecast
to be above freezing for most areas, so freeze headlines probably
won`t be necessary, but a frost advisory may likely need to be
hoisted eventually. We warm into the upper 50s to lower 60s on
Thursday, with even warmer readings by the end of the week and
weekend, especially by Sunday.

There is another system arriving by early Friday and into the first
part of the weekend. Timing has improved with this next system to
warrant likely PoPs on Friday night into early Saturday. Sunday
looks dry.

&&

.AVIATION...
Issued at 1035 PM CDT Sun Apr 18 2021

Clouds will continue to clear out tonight, with winds becoming
light. The guidance isn`t showing much in the way of fog. But it`s
something to monitor given the clearing, earlier light rains and
near calm winds through daybreak. Otherwise VFR, with winds
becoming WSW 5 to 10 kts Monday.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$




Area Forecast Discussion

National Weather Service Phoenix AZ

 459 PM MST Sun Apr 18 2021

.UPDATE...
Updated 00Z aviation discussion.

&&

.SYNOPSIS
Isolated sprinkles and showers are expected this afternoon and
evening across central Arizona as a low pressure system drifts
southward through the state. An isolated thunderstorm capable of
producing strong wind gusts is also possible. Above normal
temperatures will resume Monday with highs climbing into the low
90s across the lower deserts. Another weather system during the
middle of next week will bring a return of somewhat cooler
temperatures and increased breezy conditions.

&&

.DISCUSSION...
Latest water vapor imagery reveals cyclonic flow across Arizona
with drier air positioned across the Mojave Desert. RAP analysis
confirms the presence of a closed low at 700 mb, which is evident
on water vapor imagery across southern Maricopa and Pinal
Counties. Surface observations also suggest the presence of a
surface low or trough a bit further south. Given the positive tilt
of the upper trough, anomalously strong northeast flow is
resulting in breezy conditions across much of the forecast area.

Main impact from the aforementioned low pressure system will be
the potential for isolated convection across central Arizona this
afternoon. Latest mesoanalysis does not indicate any organized
areas of instability across the Desert Southwest, however 12z run
of the HREF and GEFS suggest max SBCAPE/MUCAPE up to 250 J/kg will
be sufficient for isolated showers and storms to develop this
afternoon.

Latest hi-res guidance including the HRRR indicates showers and
isolated thunderstorms will blossom rapidly across central Arizona
early this afternoon. Meanwhile, neighborhood probabilities
indicate the threat could extend as far west as La Paz and western
Maricopa counties as the low drifts due southward. Although
dewpoints have increased considerably since this time yesterday,
conditions remain relatively dry near the surface with dewpoints
in the 20s and 30s. This will yield strong evaporational cooling
along with areas of virga/sprinkles, and consequently an
environment favorable for downburst winds. The strongest cells
will be capable of producing gusts in excess of 40+ mph as well as
localized blowing dust. The abundant dry air will also limit rain
totals, with only a few hundredths of an inch likely in the
strongest cells. Conditions are expected to improve rapidly early
this evening as subsidence builds in behind the trough axis.

&&

.PREVIOUS DISCUSSION...
High temperatures will begin to climb on Monday and Tuesday as the
storm system moves out of the area. Tuesday will likely be the
warmest day this week with mid 90s across southeast California and
low 90s for south-central Arizona. The Imperial area shows a
10-15% chance of reaching as high as 100 F according to NBM
temperature probabilities. By Wednesday, yet another shortwave
will begin to move in from the west. WPC cluster analysis shows
that the uncertainties with this system have shrunk since
yesterday, but still revolve around how far southwest the system
will dig and how tight of a pressure gradient will develop over
the forecast area. The ECMWF ensemble firmly supports the idea of
a deeper and more elongated trough and has little overlap with
the GFS ensemble, which has a weaker trough that does not dig to
the southwest. The main implications this will have on the
forecast will be with respect to the amount of cooling we see and
how breezy conditions will become. The mostly overland trajectory
of this system along with the lack of favorable dynamic support
given its positive tilt will make precipitation unlikely, which
ensemble guidance all agree upon. ECMWF EFI shows the potential
for anomalously strong winds on Wednesday as this system
approaches. The potential for strong wind combined with dry
conditions may lead to heightened fire weather concerns. The
trajectory of this system will likely favor the strongest winds in
the Imperial area, but breezy conditions would be expected
everywhere. By Thursday, temperatures look to cool into the mid
to upper 80s for highs across the lower deserts as heights fall
with the passage of this system. Temperatures quickly rebound
going into the weekend as ensemble members show good agreement in
upper level ridging returning.

&&

.AVIATION...Updated at 2359Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Isolated convective activity will continue to dissipate over the
next hour with no showers expected by 01Z. Gusty N-NW winds that
have frequently been sustained at 10-20 knots with gusts up to
30-35 knots will continue weakening over the next hour as well,
with some variability with the winds as showers dissipate over the
East Valley. Blowing dust impacts and dust devils observed near
KIWA should begin to subside as well over the next hour with
ceilings continuing to lift above 10-15 kft and eventually
clearing after sunset. Winds will gradually become E-NE overnight
at 5-10 knots with light and variable or easterly winds tomorrow
morning before becoming westerly between 20-22Z. Winds should
generally remain below 10 knots with only very brief gusts.

Southeast California/Southwest Arizona including KIPL and KBLH:

Strong northerly 15-25 knot winds with brief gusts up to 30 knots
should subside below 10-15 knots by 02Z. Winds this evening and
overnight will generally favor N-NW headings at KBLH and more W-NW
headings at KIPL before becoming light and variable tomorrow
morning across the region. Clear skies will persist through
Monday afternoon with winds generally remaining below 10 knots.

&&

.FIRE WEATHER...
Wednesday through Sunday:
Hot, dry and windy conditions are likely Wednesday ahead of a low
pressure system. The greatest fire danger will be across southern
Arizona, where MinRHs will fall into the single digits. Conditions
will improve somewhat Thursday and Friday as temperatures and RHs
return to seasonable values. A warming trend is then anticipated
next weekend.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Hodges
AVIATION...Hopper
FIRE WEATHER...Hirsch