Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/08/19
Area Forecast Discussion
National Weather Service Grand Forks ND
927 PM CST Sat Dec 7 2019
.UPDATE...
Issued at 927 PM CST Sat Dec 7 2019
Starting to see some reports of minor vis restrictions in
northeast ND as light returns along/behind cold front star to
spread southward. This may just be flurries or very light snow,
but still can`t rule out light freezing drizzle before the
stronger period of CAA arrives later tonight. Besides minor
adjustments to near term trends, holding steady on current short
term forecast.
UPDATE Issued at 638 PM CST Sat Dec 7 2019
South to southwest flow in the lower levels is keeping WAA in
place ahead of approaching surface trough and cold front, and in
this region non measurable light freezing drizzle can`t be ruled
out before the cold front passes. RAP profiles indicate saturated
layer of 2-4 KFT depth warmer than -8C lingering in our south
through 12Z, so I can` rule out freezing drizzle remaining
possible through Sunday morning. CAA is strong enough behind cold
front that profiles should only support snow as p-type once the
front moves through an area. CAMs showing narrow progressive axis
of light measurable precip along the cold front and upstream
radars in Canada are showing light returns matching model trends.
Tendency will be a dusting at most where light snow occurs. Signal
for possible lingering flurries though behind front in CAA and
steep lapse rates.
Adjustments were made to expand mention of slight chance PoPs,
introduce mention of freezing drizzle, and linger mention of
flurries once the front passes Sunday morning.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 251 PM CST Sat Dec 7 2019
The main feature of the short term forecast period will be a
clipper system that will bring winter weather impacts to the
southern half of the CWA. Generally three to five inches of snow
are possible south of the Highway 200 corridor in the 00Z to 18Z
Monday timeframe, with winter weather impacts possible for the
Monday morning commute in larger cities such as Valley City,
Fargo, Fergus Falls and Wahpeton.
For tonight, breezy southerly winds will inhibit fog formation
despite some areas once again seeing above freezing temperatures.
There will be a break in precipitation for tonight into late
Sunday morning...as breaks in sky cover are evident on satellite
across eastern Montana and western North Dakota.
Sunday and Sunday night...increasing synoptic lift evident from
modeled Q-vector convergence increase chances for snowfall across
the region beginning around noontime tomorrow. The area of forcing
will transit the CWA from roughly 21Z Sun through 15Z Mon...with
deterministic models indicating stronger frontogentic forcing late
Sunday evening. WPC indicating a 50 per cent or greater
probability of exceeding four inches of snow...dropping to around
20 per cent at the six inch threshold. These higher amounts line
up with strongest FG forcing. Overall looking for three to five
inches of accumulation by the end of the Monday morning commute
south of Highway 200...with the highest confidence along and
south of the Interstate 94, US Highway 10 and MN Highway 34
corridor. No plans for advisory attm as further model runs narrow
down the track of the surface low.
.LONG TERM...(Monday through Saturday)
Issued at 251 PM CST Sat Dec 7 2019
The main concern for the period continues to be the well advertised
shot of arctic air to impact the region for the first half of the
work week. Relatively warmer conditions and the return to a more
active pattern will be on tap for the second half of the period.
Northwest flow aloft will be accompanied by areas of high pressure
passing through the area during the Monday through Wednesday time
frame. Although the coldest air should remain north and east of the
area, plenty of cold air advection will help bring down some of the
850 mb temperatures reaching into the -20 to -25 C degree range.
While Monday should still see high temperatures above the zero mark
(albeit maybe just barely), Tuesday and Wednesday look to bring
temperatures struggling to reach the zero mark, even during the day.
Both daytime and nighttime temperatures a good 25-30 F degrees below
normal will likely be enough to allow for an extended period of wind
chills solidly into advisory criteria even without a push of
stronger winds.
More zonal flow returns for the second half of the period with the
potential for periodic light snow chances. Confidence is low on any
high impact events with ensemble data not indicating much in the way
of QPF at this time. However, even light snow events occurring at
the right time (i.e, rush hour) could bring some level of
transportation impacts at times towards the end of the work week and
beginning of the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 536 PM CST Sat Dec 7 2019
Cold front now moving into southern Manitoba will overspread our
CWA and with this passage MVFR and IFR ceilings will overspread
eastern ND and northwest MN late this evening (after 03Z) and
continue through much of Sunday. A brief period of light snow or
even freezing drizzle can`t be ruled out tonight or Sunday
morning, but better snow chances arrive with a disturbance moving
into central and southeast ND by late Sunday afternoon and Sunday
evening. A window for VFR ceilings could occur during the day
Sunday before this system moves in. Right now best snow chances
Sunday afternoon would be KDVL, with chances increasing after 00Z
tomorrow elsewhere. Expect shifting and increasing winds behind
the cold front tonight going from south to southwest then to the
northwest. Gusts around 25kt will be possible behind this front
through midday Sunday.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
&&
$$
UPDATE...DJR
SHORT TERM...Speicher
LONG TERM...Lee
AVIATION...DJR
Area Forecast Discussion
National Weather Service Lincoln IL
834 PM CST Sat Dec 7 2019
.SYNOPSIS...
Issued at 318 PM CST Sat Dec 7 2019
Mild and dry conditions will be on tap across central Illinois for
Sunday with high temperatures topping out in the upper 40s and
lower 50s. Rain will develop Sunday night into Monday...followed
by sharply colder weather by Tuesday.
&&
.UPDATE...
Issued at 831 PM CST Sat Dec 7 2019
South winds and increasing cloud cover should help maintain a slow
temperature fall overnight. While thin cirrus is in place
currently, starting to see expanding stratus just south of St
Louis that should work into portions of central Illinois
overnight. Going forecast is in good shape this evening with no
major changes planned.
&&
.SHORT TERM...(This evening through Sunday)
ISSUED AT 318 PM CST Sat Dec 7 2019
Mostly clear skies will prevail this evening before clouds
increase overnight. An area of low-level moisture currently in
place across far southern Illinois/western Kentucky will
gradually advect northward as southerly boundary layer flow
increases. Models do not have a good handle on the moisture, but
based on current satellite trends think clouds will develop/spread
northward across the eastern half of the KILX CWA after midnight.
HRRR hints at this, indicating overcast conditions along/east of
I-55 by dawn Sunday.
A short-wave trough over British Columbia and a deep upper low
spinning off the coast of northern California will phase over the
northern Rockies...then will dig into the Plains/Midwest early
next week. As this process unfolds, downstream ridging will push
temperatures into the upper 40s and lower 50s across central
Illinois on Sunday. While deep-layer moisture will initially be
lacking, several CAMs suggest scattered light showers will develop
along/west of the Illinois River by mid to late afternoon.
.LONG TERM...(Sunday night through Saturday)
ISSUED AT 318 PM CST Sat Dec 7 2019
Once the airmass moistens sufficiently, showers will become
widespread late Sunday night into Monday as stronger forcing
approaches from the west. Warm conditions will continue on Monday
as highs once again top 50 degrees: however, once a strong cold
front passes, temps will take a nosedive Monday night. 12z Dec 7
models continue to indicate that most of the precip will end
before the cold air arrives, so only a brief period of very light
snow is expected Monday night.
The coldest conditions will arrive Tuesday into Wednesday when
highs remain in the 20s and overnight lows plunge into the single
digits and teens. The lowest wind-chills from 0 to -5 will occur
late Tuesday night into Wednesday morning. After that, all signs
point to a rapid warm-up by the end of next week as the upper
trough lifts northeastward and a zonal flow pattern re-establishes
itself across the CONUS.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 513 PM CST Sat Dec 7 2019
Ridge of high pressure that provided light winds and VFR
conditions will begin to shift east to the upper Ohio Valley with
southerly flow overspreading central Illinois in its wake. MVFR
ceilings currently over portions of the lower to mid Mississippi
Valley are forecast to expand north/northeast overnight across
central Illinois. There remains a lot of variability between
models on the placement and timing of the lower ceilings, so
timing may still need adjustments. There is low confidence in how
quickly these lower ceilings will clear, though the western
terminals will have the best chance during the day Sunday. South
winds will prevail through the period, becoming gusty during the
afternoon hours.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Deubelbeiss
SYNOPSIS...Barnes
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service San Francisco Bay Area
436 PM PST Sat Dec 7 2019
.SYNOPSIS....Showery conditions through the morning, then another
frontal band will move across the district bringing heavier
showers and a chance of thunderstorms. Lingering showers on
Sunday but trending drier by afternoon. Dry weather returns early
next week.
&&
.DISCUSSION...as of 1:09 PM PST...The next round of rain has
arrived to the North Bay. Latest KMUX radar imagery shows light to
moderate rain falling across much of Sonoma and Napa Counties as
of 1 pm PST. The rain is also starting to impact San Francisco
this early afternoon. Expect the rain to continue spreading
southeastward through the rest of the day. While we have yet to
observe any lightning strikes in the San Francisco Bay Area, the
chance of thunderstorms will continue through the evening hours
for much of the region. The Day 1 Storm Prediction Center has the
vast majority of the region in at least the general thunder
category. Additionally, most of the North Bay is under a marginal
risk for severe weather. The 18Z HRRR does indicate some locally
impressive 0-1 km bulk shear and 0-1 km storm relative helicity
values, but think the best potential for any sort of rotating
storms will be to the east of the area in the Central Valley
where the skies have thus far remained generally clear today. In
addition to the thunderstorm risk, a Flash Flood Watch is in
effect for the Kincade Fire burn area through 10 pm PST this
evening.
Southerly winds will remain locally strong through the rest of
the afternoon. Winds have already gusted above 40 mph at SFO, 31
mph at OAK, and at least 25 mph at MRY today. These winds will
diminish later this afternoon or evening near sea level with
breezy conditions likely persisting in the higher elevations into
the overnight hours.
Scattered rain showers are expected to continue through about
mid-day on Sunday as the upper level trough axis passes through
the Bay Area. Behind this trough an upper level ridge will quickly
build over the West Coast, bringing dry conditions to the Bay
Area and Central California Coast for Monday and Tuesday. Models
advertise a weak system that will impact parts of northern
California around Wednesday. At this point it would appear the
best chances for rain would be north of the Golden Gate with
perhaps a few tenths of an inch. Another system will then arrive
late Thursday or Friday to northern California, but again the best
rain chances will be to the north of the Golden Gate. Overall --
all locations are expected to be significantly drier this upcoming
week compared to the last few weeks. In fact, the latest 6-10 day
precipitation outlook (valid December 13-17) from the Climate
Prediction Center places much of central and southern California
with favored odds of experiencing below normal precipitation.
&&
.AVIATION...as of 4:36 PM PST Saturday...Generally MVFR except
IFR ceilings and visibilities in a band of heavy showers with a
low level cold front coupled to an amplifying 700 mb trough
pressing eastward over the Bay Area; echo tops 20 thousand feet
with isolated tops to 25 thousand feet, lightning strikes so far
observed east of our cwa. Additional amplification in the 700 mb
trough including the trough at 500 mb tonight and Sunday generates
more showers. Drier weather returning by the end of the 00z taf
cycle.
With convergent winds focusing low level isotherms together, i.e.
frontogenesis expect gusty prefrontal south winds to continue into
the early evening before diminishing. Surface winds forecast to
shift to southwest and west direction, but timing is low confidence
due to initially mature and closed 500 mb low offshore transforms
to an open wave before passing eastward over the cwa Sunday morning.
The mid level trough axis will move east of the cwa Sunday afternoon
with dry weather returning.
Vicinity of KSFO...MVFR ceiling with showers, possibly heavy, through
03z this evening, surface wind direction close to 210 degrees with
winds subsiding by 03z. Best guess is that the surface wind will
wait until late evening or early Sunday morning before shifting to
240 degree wind direction. West wind late Sunday morning at latest.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR-MVFR ceilings with showers, possibly
heavy at times, surface wind from the south. MVFR tonight with
showers. Winds shifting to west to northwest by Sunday afternoon.
&&
.MARINE...as of 12:59 PM PST Saturday...A secondary frontal
boundary will move through the coastal waters today. Scattered
thunderstorms will move into the coastal waters which could
produce lightning, gusty winds, and possible waterspouts. Breezy
to gusty south to southwest winds will continue through the day
today before diminishing this evening. A moderate west swell will
continue through Sunday. Steep wind waves will continue through
the day today creating hazardous seas.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Flash Flood Watch...CAZ506-507
SCA...SF Bay until 9 PM
SCA...Mry Bay until 9 PM
SCA...Pt Arena to Pt Reyes 0-10 nm until 9 PM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 9 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
&&
$$
PUBLIC FORECAST: Rowe
AVIATION: Canepa
MARINE: BFG
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Area Forecast Discussion
National Weather Service Shreveport LA
808 PM CST Sat Dec 7 2019
.AVIATION...
Low stratus and reduced vsbys continue to hang around at KMLU and
has now moved over KELD resulting in IFR/LIFR conditions. High
cigs and VFR conditions continue to prevail across the remaining
TAF sites. However, low cigs will continue to push westward and
additional low clouds will develop overnight across the remainder
of the TAFs resulting in reduced flight categories. Low cigs
should lift toward the end of the TAF period resulting in VFR
conditions. /20/
&&
.PREV DISCUSSION... /issued 302 PM CST Sat Dec 7 2019/
SHORT TERM.../Tonight through Sunday Night/
The latest RAP analysis indicates that the area is in a west-
northwesterly mid-level flow. At the surface, a 1009mb surface low
is located along the Front Range of Colorado while high pressure
extends from the Ohio/Tennessee Valleys southwestward into the
ArkLaTex. In addition to high pressure across the local area, a
deep layer of dry air is in place with moisture limited to the
1000-900mb layer. A pocket of stratus is lingering over the
ArkLaMiss and eroding from the west. Elsewhere, aside from some
thin cirrus skies are mostly sunny.
There is HRRR/NAM 3km agreement that the mid-level flow will
become more zonal tonight through Sunday night as the surface
high pulls well northeast of the area and the low swings from the
Front Range across the Plains into eastern Oklahoma by Monday
morning. A 900-500mb layer of dry air will remain in place tonight
through Monday morning, keeping the forecast dry. Similar to the
last two nights, stratus and some patchy fog will develop during
the pre-dawn hours Sunday and Monday and will be slow to burn off
each day. As the surface low moves into Oklahoma, ahead of it,
winds at 5 to 10 mph will become more southerly Sunday into Sunday
night.
For temperatures, some radiational cooling will occur tonight
before stratus builds back in, allowing temps to cool to the
lower to mid 40s across the area. High temps are closest to the
National Blend of Models (NBM) on Sunday with highs ranging from
the lower 60s in McCurtain County, Oklahoma to the upper 60s along
the I-20 corridor to the lower 70s in Deep East Texas and central
Louisiana. With an enhanced southerly flow and some warm air
advection on Sunday night, overnight lows will range from the mid
to upper 50s across much of the area. /04-Woodrum/
LONG TERM.../Monday through Saturday Night/
A progressive pattern to continue through the second week of
December with two short wave trough passages scheduled for the
middle of next week and next weekend.
The first positively tilted trough approaches by Tuesday afternoon
with rain chances increasing accordingly through Wednesday. This
trough amplifies during as it traverses across the ArkLaTex region
likely producing widespread rain, showers, and perhaps even a TSTM
mainly down south across central LA.
After this trough passage, we can expect a brief break for Thursday
and early Friday, before another trough passage is forecast for late
Friday through next Saturday and early Sunday.
Temperatures during the middle of the week behind the first frontal
passage approach freezing across SE OK and SW AR. For the moment,
it appears that as the colder air advects SE into the Ouachita and
Kiamichi Mountains, the precipitation should have ended across SE OK
and SW AR. Thus will not mention any frozen or freezing
precipitation. Nevertheless, as the event approaches and can
further finalize the timing of cold air arrival and precipitation
ending, will further define for any mention of wintry precipitation.
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 44 68 57 75 / 0 0 0 10
MLU 45 68 55 75 / 0 0 0 30
DEQ 41 63 53 71 / 0 0 0 20
TXK 43 64 56 72 / 0 0 0 20
ELD 41 66 54 72 / 0 0 0 20
TYR 46 69 58 75 / 0 0 0 10
GGG 44 69 58 76 / 0 0 0 10
LFK 45 71 59 77 / 0 0 0 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
20