Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/26/17
Area Forecast Discussion
National Weather Service Denver/Boulder CO
714 PM MDT Wed Oct 25 2017
.UPDATE...
Issued at 638 PM MDT Wed Oct 25 2017
Models show a decent mountain wave developing overnight. NAM12
spatial cross-sections show a 40 kt cross wind component sliding
down the east slopes through 09z, while the RAP13 shows a 30 kts
component. Both show the wave breaking down after 09z ahead of
the arrival of the cold front. Main adjustment was to increase the
winds in znes 35, 36, 38 and 39. Peak wind gusts 45-50 mph in the
windiest locations. I also modified the overnight lows by a
couple of degrees in the windier areas as well.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 304 PM MDT Wed Oct 25 2017
The record high temperatures today will be a distant memory
tomorrow as a major change in our weather is coming starting
Thursday morning. First, tonight`s weather is relatively benign.
Strong northwest flow aloft will pick up upstream of a potent
short wave trough over the northern Plains. As the northwest aloft
increases, winds across the mountains and foothills will also
increase, and with high level clouds increasing...tonight`s low
temperatures will remain fairly warm. The high temperature for
Thursday is most certainly going to occur at midnight tonight for
reasons immediately below.
A fast moving short wave trough will move southeast out of
Wyoming during the day Thursday in the strong northwest flow.
There is a 4-6 hour period of lift associated with the short wave
trough, moving north to south across our area. At the surface,
the strong trough across the northern Plains will drive a strong
cold front across the Plains of Colorado. Models in general are
too slow and not strong enough with the cold air behind the front.
HRRR and the ESRL HRRR seems to come closest on timing and
strength. Current thinking is the pre-frontal wind shift front
will entire the state from Wyoming around 6 AM, impact metro
Denver around 8 AM, and Limon around 9 AM. The dramatic increase
in north winds should occur an hour or two after the initial wind
shift. Expecting north winds 25-35 with gusts to 45 mph along and
east of I-25. Winds will stay up through Thursday evening. In
terms of precipitation amounts and type, the amount of moisture
behind the front is not impressive and the moisture associated
with the short wave trough is also pretty weak. Upslope flow is
shallow, just in the lowest 2-3 kft feet AGL. Finally, with the
rapid movement of the trough southward, expect only light
precipitation for 4-6 hours mainly from I-25 and west into the
foothills and mountains, and along the Palmer Divide where much
better upslope will occur. Temperatures will be falling behind the
front into the upper 30s across the Plains below 6500 feet. Any
additional cooling from evaporation should quickly change any
light rain showers over to snow within an hour or less. Above 6500
feet any precip that falls should start out as snow. Best chance
of accumulating snow will be across the eastern slopes of the
Front Range foothills and mountains, and the Palmer Divide. QPF
is low enough that no highlights will be needed for the snowfall.
Fort Collins to Denver could see a trace to an inch. The Palmer
Divide 1-2 inches, and 2-4 inches for the Front Range Foothills.
One thing to note is that despite fairly warm road temps, even
light snow with 30-40 mph gusts would reduce visibility and
potentially create hazardous driving conditions across the Palmer
Divide in particular, but elsewhere across the I-25 corridor.
Across the mountains, the easterly component upslope will be
confined to below 9000 feet, thus the main forcing available will
be synoptic with the strong cooling at 700 mb and above. This
forcing arrives midday. Should be cold enough for snow
everywhere, but the best accumulating snow will be along the Front
Range Mountains, where 2-5 inches are possible in ~6 hours. Snow
should wind down for all of our area by midnight, with Park
County seeing snow end the latest.
.LONG TERM...(Thursday night through Wednesday)
Issued at 304 PM MDT Wed Oct 25 2017
Overall north to northwest flow in high amplitude pattern with ridge
over west coast and trough over the east-central US. Long term
period begins Thursday night with surface front well south of the
region and gusty north winds and strong cold air advection. 500
mb trough extends from surface low over Minnesota with trough axis
stretching southwest across Colorado. Upper trough axis quickly
swings out of area by 06z Friday, with lingering mountain
snow showers dissipating and little additional accumulation. Cold
night Friday night in the 20s on the plains and teens in the
mountains, well below normal but still well above record
territory. Friday still under cold air advection northerly flow
and below normal temperatures. Another cold night Friday night and
start to Saturday, then low level flow turns westerly downslope
with moderating temperatures into the 50s on the plains and 40s in
the mountains.
Saturday another weak disturbance at 500 mb swings through the
region in northerly flow. A small uptick in layer RH, and enough
orographic lift in the mountains to generate slight chance to chance
pops in the mountains.
Northwesterly flow continues the rest of the weekend in to early
next week. Given strong flow aloft gusty winds in the mountains not
out of the question. Temperatures continue to moderate to near
normal Sunday with a return to southerly flow. Another cold front
passes Monday, lowering max temps. For Tuesday another shortwave
trough brushes the region with slight chance to chance pops starting
after midnight Tuesday. Mainly snow showers, but may mix with rain
on the plains.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 638 PM MDT Wed Oct 25 2017
VFR conditions through about 16Z across the metro area terminals.
Westerly flow at DEN and APA should eventually turn more to the
southwest by 04z, then back northwest after 08z ahead of the
approaching cold front. Gusty westerly winds may persist at KBJC
until 09z, then decrease as the wind switches to the northwest.
Aviation impacts expected tomorrow morning with a strong cold
front arriving around 16Z. North winds behind the front could gust
to 30-35 kts at DEN, 25-30 kts at APA and BJC during the
afternoon hours. CIGs will drop with stratus behind the front, but
should remain MVFR, albeit lower MVFR. Light snow possible at all
three terminals, but highest potential at KBJC and KAPA. Vsbys
could reduce visibility to around 2 SM during the afternoon
hours. No snow accumulation is expected on the runways/taxiways,
though APA and BJC could see around an inch on grassy surfaces.
DEN could see a trace but chances are lower for any accumulation
on grass. Any snow should end between 00-03Z and CIGs should
remain MVFR and winds will stay strong out of a northerly
direction through 00Z tomorrow.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Cooper
SHORT TERM...Schlatter
LONG TERM...Hanson
AVIATION...Schlatter/Cooper
Area Forecast Discussion
National Weather Service Grand Forks ND
1010 PM CDT Wed Oct 25 2017
.UPDATE...
Issued at 1009 PM CDT Wed Oct 25 2017
00z nam and namnest coming in a bit drier with their western edge
of precipitation in the colder air Thursday. This leads to less
confidence of snow/wind combo. Wind is a given 50 kts will easily
mix down during the midday-afternoon in the RRV. Snow is a huge ?
and it is hoped further examination of data overnight can lead to
some better confidence in terms of wind vs winter headlines.
UPDATE Issued at 709 PM CDT Wed Oct 25 2017
Latest HRRR quite consistent with sfc low just south of Grand
Forks near 09z then to near Mahnomen MN 12z. Precipitation stays
well north of the low track...though a few light showers are
possible right with the actual front/low itself. But the main show
comes as precipitation north of the low wraps back west around the
low and drops south. I see nothing in the latest data this early
evening to change the fcst. The uncertainity in regards to ptype
and snow amounts remain highly uncertain in timing and intensity.
Wind is a given...but how low will vbsy go in the high wind area
for blizzard conditions? That is the main unknown.
&&
.SHORT TERM...(This evening through Friday)
Issued at 308 PM CDT Wed Oct 25 2017
High wind and potential winter impacts the main concern for later
tonight into Thursday and Thursday night. Confidence is high in
the synoptic pattern and resultant impacts, but confidence is
lower in the details concerning winter weather impacts. 12z models
in good agreement with the track and magnitude of this system
(although the GFS is a bit different). At any rate, high wind
ingredients (pressure rise/fall, mixing layer depth, cold air
advection, magnitude of wind aloft) all indicate the potential for
gusts up to 60 mph. Thus, confidence is high for warning criteria
winds along and west of the Red River Valley. Uncertainty starts
to creep in with winter weather impacts. Two main areas of
uncertainty. 1) Red River Valley counties and possible blizzard
conditions. Blizzard conditions will require a persistent light
snow, which seems very possible across the northern valley in the
deformation zone forcing. Persistent snow seems less certain to
the west and south of this region. Warmer air temps, warm ground
temps, and an early season system lead to lower confidence in the
magnitude of this winter weather impact. 2) Heavy snow across
northwest Minnesota. This region will be in an area of stronger
synoptic forcing (given the track of the mid-level low), with the
potential for mesoscale forcing. Models giving QPF values 0.50
inch to just over an inch. The main question will be how quickly
the below freezing low level airmass advects into the region
(changing rain to snow). NAM typically does better, and does show
this airmass advecting in quicker (more snow), while the ECMWF/CMC
are warmer for longer (less snow). Given these uncertainties,
will keep the watches in effect where winter weather impacts seem
most likely. Further west, winter weather impacts seem less
certain and issued a high wind warning.
.LONG TERM...(Friday night through Wednesday)
Issued at 308 PM CDT Wed Oct 25 2017
Impacts for the weekend into the first part of next week will center
on temperatures and the possibility of some light rain mixing over
to snow Sunday night into Monday with a "polar" low sinking to Lake
Superior restricting most of the pcpn to NW MN. Upper low then
swings away to the northeast leaving north to northwest flow in its
wake for a couple of days. Accordingly, NAEFS ensembles depict lower
than average 850 hPa temps right on through the period, translating
to daytime highs from the upper 30s to mid 40s with overnight lows
mainly in the 20s. There is a hint of moderating toward normal Wed
with a shot of pcpn of Pacific origin possible by then.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 709 PM CDT Wed Oct 25 2017
Big changes occur late tonight into Thursday as storm system moves
east-southeast across the region in the 06z-15z period. Winds will
turn north-northwest beind the low with highest wind speeds in the
RRV and DVL basin where gusts to 50 kts very likely mid morning
thru the afternoon. Vsbys reduced in snow and MVFR cigs.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...High Wind Warning from 6 AM to 10 PM CDT Thursday for NDZ006-014-
024-028-038-049-052.
Winter Storm Watch from 10 AM CDT Thursday through Friday
afternoon for NDZ007-008-015-016-026-027-029-030-039-053-
054.
MN...Winter Storm Watch from 10 AM CDT Thursday through Friday
afternoon for MNZ001>009-013>015-029-030-040.
&&
$$
UPDATE...Riddle
SHORT TERM...TG
LONG TERM...WJB
AVIATION...Riddle
Area Forecast Discussion
National Weather Service Northern Indiana
842 PM EDT Wed Oct 25 2017
.SYNOPSIS...
Issued at 241 PM EDT Wed Oct 25 2017
Clearing skies and light winds will allow temperatures to fall into
the low 30s tonight with widespread frost. Some locations across
northwest Ohio and far southern lower Michigan may drop into the
upper 20s. Thursday into early Friday will feature a brief
warming trend before a strong cold front brings renewed chances
for rain later Friday into Saturday. Much cooler air will funnel
in behind this front for this weekend.
&&
.UPDATE...
Issued at 834 PM EDT Wed Oct 25 2017
Ridge axis moving across the region this evening allowing winds to
decouple and temps to fall rapidly. A few sites across the east
dropped 4 to 6 degrees last hour and already into middle 30s.
Latest RAP and HRRR drop Tds across NW Ohio into upper 20s with
low temps to around 30. short term hires model guidance not
surprisingly is lagging in the rapid drops and appear too warm
primarily in the east. With longer duration at or below freezing
now expected along with some outlying upper 20s in NW Ohio, have
upgraded to a freeze warning overnight. Further west, temp
forecast complicated by passing ridge axis and warm air advection
developing over top inversion with weak gradient developing late.
This may be enough to steady lows right around freezing and
current grids has this handled. Duration at or just below freezing
looks short lived and with frost advisory already up with mention
of brief freezing temps have opted to stay with frost advisory
given little change in impacts for headline changes.
&&
.SHORT TERM...(Tonight through Friday night)
Issued at 241 PM EDT Wed Oct 25 2017
Low level ridging builds in tonight with decoupling and mainly clear
skies expected. Thus a good radiational cooling event likely with
temps bottoming in the low 30s and widespread frost.
Potent pv anomaly cutting through wrn Canada this aftn will amplify
quickly sewd through the upper midwest tomorrow. Ewd sharpening
baroclinic zone will activate by late aftn commensurate with nwd
Gomex origin low level moisture surge. Primary preference still lies
with general wwd bent spectral solution scope spinning up an intense
but narrow frontal induced rain band 21-00Z and slower ewd
progression tied to developing frontal wave transecting from nrn KY
late Fri into se MI by daybreak Sat. Thus will hold very close with
prior w-e pop gradient/timing delineation although intermediate
trends would suggest some erosion in both pops and temps warranted
through wrn zones late Fri.
&&
.LONG TERM...(Saturday through Tuesday)
Issued at 241 PM EDT Wed Oct 25 2017
Expansive dryslot will overspread the area Sat as frontal rain band
shifts east into the ern OH valley. Some lake response may develop
as early as Sat aftn over far sw MI pending ewd extent of lagging
upper trough however far better prospects Sat night and Sun as upper
trough lifts out through wrn MI and low level flow veers more wrly
across lake MI. Elsewhere substantial post front low level cold
advection wing will deepen across the area with chilly temps
persisting through much of the period especially as secondary
disturbance rotates through the nrn lakes Mon and solidifies deep
layer troughing across the lakes. Given progged H85 neg temp
anomalies and expected copious lake based stratocu tough to argue
against siding with coldest scope of guidance temps versus
optimistic looking blend and will hedge most periods lower.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 722 PM EDT Wed Oct 25 2017
Dry air will be across the area during this forecast period so
VFR conditions are expected. Winds will also be becoming calm
overnight before coming out of the southeast on Thursday.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Frost Advisory from 2 AM EDT /1 AM CDT/ to 9 AM EDT /8 AM CDT/
Thursday for INZ003>009-012>018-020-022>027-032>034.
MI...Freeze Warning from 2 AM to 9 AM EDT Thursday for MIZ081.
Frost Advisory from 2 AM to 9 AM EDT Thursday for MIZ077>080.
OH...Freeze Warning from 2 AM to 9 AM EDT Thursday for OHZ001-002-004-
005-015-016-024-025.
LM...NONE.
&&
$$
UPDATE...Lashley
SYNOPSIS...T
SHORT TERM...T
LONG TERM...T
AVIATION...Roller
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Area Forecast Discussion
National Weather Service Melbourne FL
910 PM EDT Wed Oct 25 2017
.DISCUSSION...
No sig WX overnight as high pressure over the GOMex maintains a
brisk NW flow over the region that will tap a very dry and stable
airmass. Sfc dewpoints largely in the L/M40s, except along the
immediate coast where a few readings were in the L50s...a 24hr
change of 25-30 degs. Evening RAOBs measured PWat values btwn 0.25"-
0.50" statewide minus the Keys...with all stations showing a 20-30C
subsidence inversion in the H85-H70 lyr. Rap analysis showing avg
dewpoint depressions thru the H85-H50 lyr btwn 30-40C. A clear case
of "severe clear".
Geostrophic approximation tables suggest the current pgrad acrs the
peninsula will support arnd 10KTS of sfc wind. However, with diurnal
heating gone and with such dry air in place, anticipate some
radiational cooling will bring sfc winds down to AOB 5mph overnight.
Indeed, latest sfc obs show many sites already there. Fcst mins in
the M40s/L50s may actually be a few degs too warm in some spots.
However, changing the fcst under current WX conditions would be
largely transparent. No updates planned this evng.
&&
.AVIATION...Thru 27/00Z.
Sfc Winds: Thru 26/03Z...W/NW 7-11KTS bcmg W/NW 3-6KTS. Btwn 26/12Z-
26/15Z...bcmg N/NW 6-9KTS. Btwn 26/17Z-26/19Z...coastal sites bcmg
N/NE 7-11KTS. Btwn 26/20Z-26/22Z...interior sites bcmg N/NE 6-9KTS.
WX/Vsbys/Cigs: VFR all sites.
&&
.MARINE...
No sig changes to the aftn package as high pres centered over the
wrn GOMex maintains a brisk NWrly breeze over the lcl Atlc that will
generate poor to hazardous boating conditions. Advisory and
cautionary statements will continue overnight as a moderate to fresh
NW breeze maintains 3-5FT seas nearshore and 5-7FT seas offshore...
dominant pds AOB 6sec.
&&
.CLIMATE...
Record Low temperature for October 26:
SITE RECORD YEAR
DAB 44 1982
MCO 41 1926
SFB 45 1982
MLB 47 2005
VRB 48 2005
FPR 49 2005
Listed below are the dates showing the last time local
min temperatures were below 50, 60 and 70 degrees this year...
50 DEGREES 60 DEGREES 70 DEGREES
DAB 04-09-2017 05-27-2017 06-03-2017
FPR 04-08-2017 05-08-2017 05-28-2017
VRB 04-08-2017 05-08-2017 06-16-2017
MLB 04-08-2017 05-08-2017 05-28-2017
MCO 05-07-2017 05-27-2017 06-28-2017
SFB 04-09-2017 05-07-2017 05-28-2017
All locations will have readings below 60 degrees on 10-25 or 10-26,
which is slightly later than average for the season. A few places
are also forecast to go below 50 degrees for the first time this
season, which would actually be earlier than average.
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory until 10 AM EDT Thursday for Flagler Beach
to Volusia-Brevard County Line 20-60 nm-Sebastian Inlet to
Jupiter Inlet 20-60 nm-Volusia-Brevard County Line to
Sebastian Inlet 20-60 nm.
&&
$$
Update/Aviation...Bragaw
Impact WX/Radar...Volkmer