Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/07/20
Area Forecast Discussion
National Weather Service Denver/Boulder CO
810 PM MST Mon Jan 6 2020
Issued at 806 PM MST Mon Jan 6 2020
Main concern tonight through Tuesday morning revolves
around the high wind potential for the foothills. Current
observations showing wind gusts mainly ranging in the 30-50 mph
range with a few higher gusts around 60 mph. Radar imagery showing
some enhancement of mountain wave across western Boulder county with
highest winds remaining over higher elevations.
Latest water vapor imagery and QG diagnostics indicate best
subsidence will be after midnight tonight through mid morning on
Tuesday and this will coincide with best shear profile for an
amplified mountain wave. In addition, forecast soundings indicate
strengthening stable layer at 750 mb through the night. Latest
HRRR showing peak wind gusts between 08z-15z with max speeds of
60-70kt during this period. Will maintain the high wind warning
through Tuesday morning. Elsewhere, winds have decreased over the
plains but still some gusty winds up to 35 mph, mainly near the
UPDATE Issued at 451 PM MST Mon Jan 6 2020
Have issued a high wind warning for the Front Range foothills for
tonight through Tuesday morning. Looks like another shot of high
winds for the foothills tonight through Tuesday morning. Local
wind programs are favoring high wind gusts up to 75 mph tonight.
This event will be more of a chinook type wind as forecast soundings
showing increasing stability at 750mb while cross sections showing
cross barrier flow increasing to 50-60 this evening. The subsident
flow will not be as strong as the past 2 nights but QG products
still showing max subsidence at 12z on Tuesday in the light to
moderate range. Shear profile also expected to improve this
evening for an amplified mountain wave as the 100kt jet over us
now will shift east of Colorado while nose of next jet segment
noses into the Nebraska Panhandle by 12z Tuesday. High resolution
models of HRRR/RAP showing potential of 60-70kt wind gusts
through about 15z on Tuesday, with best potential for the damaging
winds after midnight tonight.
.SHORT TERM...(This evening through Tuesday)
Issued at 123 PM MST Mon Jan 6 2020
Strong winds continue across the northeast plains of CO this
afternoon with moderate mid level subsidence over the northeast
plains with peak gusts in the 50-60 mph range earlier today but
those stronger gusts are becoming more localized. Will continue
with the High Wind Warning this afternoon but see the stronger
gusts start to gradually weaken the rest of the afternoon, as the
upper trough continues to shift eastward. Highway cams not showing
much in the way of impacts regarding snow and strong winds in the
mountains so have cancelled the Winter Weather Advisory. Models
still show some residual moisture in the high country overnight so
will keep isolated to scattered snow showers mentioned on the
higher northwest facing slopes, but dry elsewhere. In and near the
foothills, strong and gusty downslope winds will continue overnight,
with localized gusts in the 60-70 mph range possible. Since these
stronger gusts should be more localized, no additional high wind
highlights planned for the foothills tonight. Dry northwesterly
flow can be expected through the day on Tuesday. It will remain
windy in the mountains and foothills but the magnitude of the peak
gusts will be less, around 50 mph. Over the northeast plains,
breezy at times with temperatures back above normal, in the lower
to mid 50s.
.LONG TERM...(Tuesday night through Monday)
Issued at 350 PM MST Mon Jan 6 2020
Upper ridging is over the forecast area Tuesday night. West-
southwesterly flow aloft is in place Wednesday with an upper
through to move into the CWA late day. The upper trough axis is
just east of the CWA by 12Z Thursday morning. Southwesterly flow
aloft comes after that with the next upper trough getting into the
CWA by 12Z Friday morning. There is weak upward vertical velocity
over the CWA Tuesday night. It gets a bit stronger on Wednesday.
By late Wednesday evening, subsidence is over the forecast area.
Upward motion returns later Thursday through Thursday night. The
low level winds are a mix of normal diurnal trends and downsloping
much of the time. Concerning high winds, there is a bit of a
mountain wave set-up Tuesday night, but it is not significant.
For moisture, it is sparse Tuesday into Wednesday. By Wednesday
evening, it increases in the mountains. This continues Thursday,
with some moisture getting into the plains later in the afternoon.
There is fairly deep moisture in place over much of the CWA
Thursday night into Friday morning. There is no measurable
precipitation on the QPF fields until late Wednesday. There are
some limited amounts over the plains areas Wednesday night
through Thursday night. There is a tad over some of the plains
Thursday night. No pops through Wednesday morning. Will go with
"chance"s in the mountains Wednesday night into Thursday morning,
then "likely"s Thursday afternoon and evening. For the plains
willsgo with "slight chance"s Thursday night. No highlights. For
temperatures, Wednesday`s highs are 1-3 C warmer than Tuesday`s
readings. Thursday`s highs are 1-4 C cooler than Wednesday`s. For
the later days, Friday through Monday, models have the upper
trough pushing east of the CWA by Friday evening, with upper
ridging moving in. By late Saturday, continuing into Monday an
upper trough is over the CWA. It is unsettled, with mainly snow
for the mountains through the weekend.
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 806 PM MST Mon Jan 6 2020
VFR with some mountain wave cloudiness through Tuesday morning.
Surface winds will be erratic through the morning given the
mountain wave formation with strongest winds expected at BJC,
especially after midnight. Could see some of the stronger winds
spread out towards DIA later tonight/Tuesday morning but overall
confidence is low to medium. Overall winds will decrease Tuesday
afternoon and less winds then we had today.
High Wind Warning until noon MST Tuesday for COZ035-036.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
522 PM CST Mon Jan 6 2020
.SHORT TERM...(This evening through Tuesday)
Issued at 1229 PM CST Mon Jan 6 2020
Aloft: Animations of WV imagery and RAP tropopause analyses
indicated modestly-amplified zonal flow over the CONUS. A wk
shrtwv trof was over the Nrn/Cntrl Plns. As this trof heads into
the TN Vly tonight...some amplification will occur in its wake in
combination with a ridge building along the W coast. As a
result...W flow will become NW over NEB/KS.
Surface: 1024 mb high pres was over the OH Vly. A wk trof was
moving thru NEB/KS associated with the feature aloft. This trof
will move E along with its upr-lvl counterpart. High pres will
emerge into TX and strengthen to 1030 mb. The influence of this
high will extend N into NEB/KS.
Rest of this afternoon: Sunny. Mild temps with highs in the 40s.
W-NW winds will be gusty at times...espcly W of Hwy 281.
Tonight: Mostly clr this evening...then incrsg mid-high clds
after 06Z. Lows still above normal...mostly in the 20s.
Tue: Partly-mostly cldy to start but becoming sunny. Highs svrl
degs above normal with 40s over S-cntrl NEB and low 50s over
.LONG TERM...(Tuesday night through Monday)
Issued at 249 PM CST Mon Jan 6 2020
Aloft: The ridge building along the W coast tonight will advance
E and crest over the Plns Wed morning. A shrtwv trof will follow
Thu morning. This trof will initiate a pattern change...with a
longwv trof dvlpg and becoming locked-in over the Wrn USA. The
flow over NEB/KS will remain from the SW thru Mon. A shrtwv trof
is fcst to eject out of the mean Wrn trof Fri night...and there
may be another 1 or 2 thereafter...but mdl disagreement within the
broad Wrn trof lowers confidence on timing.
Surface: A cold front was currently over Cntrl Can. This front
will move S and E. It will move into NEB/KS late Tue and stall
from NW-SE. Meanwhile...a cool front will move onshore in the W.
This front will cross the Wrn USA and advance acrs NEB/KS Wed
night. Low pres will form along this front and head acrs the
GtLks. This will yank truly cold air S into the Cntrl Plns
Fri...with strong high pres over the Nrn Plns. Return flow will
dvlp Sat-Sun as that high moves into the Ern USA. It appears the
next cold front could move thru next Mon.
Temps: Continued milder than normal thru Thu...then turning
colder beginning Fri. Fri-Sat will be colder than normal. Sun-Mon
are uncertain...but probably will trend back to near normal.
Cold Outlook: Believe this upcoming cold snap is just the
beginning. Since mid Nov we`ve had it pretty easy in the temp
department. Temps have averaged way above normal for the last 7
weeks...and temps typically swing back-and-forth on 30-60 day
cycles. So we are due for a big downturn that it likely to last a
while. All of the operational mdls and their ensemble means
(EC/GFS/Bias-corrected GFS/CMC/JMA - Japanese Met Agency) are
fcstg the PNA pattern turn strongly negative and remain negative
for the foreseeable future. A -PNA pattern has a deep Wrn USA trof
which favors colder temps here as the mean polar front becoming
stalled just S and E of the CWA. Some of this cold will be Arctic
in nature at times. Expect to eventually see a lot more daytime
highs below frzg.
Since this warm spell began...GRI has only seen 11 days with
highs at or below frzg.
Precip: Basically dry. There might be some snow shwrs or flurries
Snow: we need to watch Fri and Fri night for accumulating snow
potential. There are a non-trivial number of EC and GFS ensemble
members that indicate a lgt-mod snowfall could occur. Some
operational EC runs have shown this potential over the last 3
days. However...there is no run-to-run consistency. It will all
depend on how the upr trof evolves...whether it wraps up and
strengthens...or it remains suppressed with the precip shield SE
of the CWA. Even if that occurs...some members are still
indicating a lgt snowfall with the Nrn stream part of the trof.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 520 PM CST Mon Jan 6 2020
Quiet weather with VFR conditions are forecast for this TAF
period. Main concern lies with LLWS, which looks to occur right
off the bat. Have LLWS in through 07Z, with models in good
agreement with the potential tapering off after that time.
Otherwise, generally westerly winds are expected through the mid-
morning hours tomorrow, before turning more northwesterly for the
final few hours of this TAF. Speeds look to top out around 10-15
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
948 PM EST Mon Jan 6 2020
Surface low pressure was strengthening over the MS/AL/TN border
region this evening. Satellite imagery shows an expansive stratus
shield spreading into eastern Tennessee over the last few hours,
with further evidence of a strengthening system noted in an area
of cooling cloud top temperatures on infrared imagery. Regional
radar composites show some isolated to scattered returns showing
up in northeast Mississippi, as well as northward into middle
Tennessee. This matches up well with the latest HRRR and RAP model
runs, both of which show precipitation filling in rapidly over
the next 3-4 hours.
There`s not much to change with the evening update, at least not
anything that would represent a meaningful difference to the
forecast. Models continue to indicate that showers will spread
across the forecast area between midnight and roughly 6 am.
Temperatures will be too warm to support any wintry precip
reaching the ground initially, but as the system and associated
cold front pass through around daybreak the column cools quickly
and a changeover to a rain/snow mix will be possible on the back
side of this disturbance in the northern areas. There remains a
healthy amount of uncertainty with how this will play out though.
By the time model soundings show a profile supportive of a wintry
mix making it below 3000 ft in elevation or so, moisture levels
aloft will be drying out rapidly, leading one to wonder how much
wintry precipitation there will be at all outside of the
mountains. Given the level of uncertainty, still think the best
way to handle this for the time being is the SPS that the day
shift issued. Overall the forecast is on track and will freshen up
the SPS and zones shortly.
/ISSUED 646 PM EST Mon Jan 6 2020/
SHORT TERM...(Tonight and Tuesday)...Difficult forecast for tonight
as a fast moving weak low pressure system tracks east-northeast
across our area, bringing a quick shot of precipitation. Precip
type should be all rain for much of the area, but northern areas and
especially some of the higher terrain is a more difficult call.
Ensemble guidance has been trending toward a much lower probability
of significant snow, and a look at model soundings indicates that
the warm air will not be pushed out until shortly before drying
begins. Confidence is not high on snow totals for areas like SW VA
and the central/northeast mountain peaks, but will show these areas
mixing with and changing to snow with some light accumulations. Will
issue an SPS highlighting this snow potential, but confidence is
still too low to issue any advisory at this point.
The precipitation will end fairly quickly with a mostly dry
afternoon Tuesday as clouds decrease. Temperatures will still be
near seasonal normals on Tuesday.
LONG TERM...(Tuesday night through Monday)...No impactful
weather is expected mid and late week, but periods of heavy rain
will occur from the end of the week into the weekend with temps
much above normal.
The mid/upper trough across the eastern CONUS will lift out Tues
night and Wed allowing heights to rise across the TN valley and
southern Appalachians as surface high pressure slides into the deep
South. Clearing skies and a relaxing pressure gradient Tues night
will allow for the coldest night of the week with lows dipping into
the upper 20`s/low 30`s. The low level flow gradually veering to
southeasterly Wed as the surface high slides farther ESE combined
with continued mostly clear skies will boost highs into the upper
40`s to near 50 across northeast TN, southwest VA, and the northern
plateau with low/mid 50`s across the central and southern valley and
Strong mid/upper longwave troughing digging into the Rockies Wed
night and Thurs will amplify strong ridging over the eastern CONUS
with the axis of the ridge shifting east with time. The surface high
will shift offshore of the SE coast, so this pattern will cause
strengthening deep layer southerly flow and WAA. Lows will stay in
the low/mid 30`s in most areas Wed night warming into the mid/upper
50`s Thurs with a few 60 degree readings likely.
As the western CONUS trough shifts farther east into the Plains
Thurs night, surface low pressure will move across the upper Midwest
and northern Great Lakes dragging a cold front toward the
Mississippi and OH valleys. East coast ridging will hold strong, so
this frontal boundary will become quasi-stationary across the
Mississippi and OH valley regions Fri into Sat. Strengthening
southwesterly H3 jet dynamics as energy emanates from the base of
the trough will parallel this boundary Fri and Sat causing strong
dynamic forcing and tremendous moisture transport to our west with
PWATs exceeding the maximum daily values. This will set up a swath
of heavy rainfall over those areas. The question remains how much
rain will we eventually see in the southern Appalachians region as
the upper trough and surface front finally shift through? Increasing
isentropic upglide will generate expanding shower coverage late
Thurs night through Fri, but this rain will be light. The heaviest
rain will move in Fri night through early Sat night as cyclogenesis
takes place in the Ark-La-Tx and tracks NE increasing the forcing
across our region. WPC QPF across our region Thurs night through
early Sun has trended much lower today with generally 1 to 2.25
inches west of I-75 and 0.50 to 1 inch farther north and east. This
seems reasonable given that the GFS is starting to trend more toward
the slower and stronger scenario that has been advertised by the
ECMWF the past few days regarding the final shortwave that will
eject from OK to the OH valley between Fri night and Sat night
causing the aforementioned surface cyclogenesis and finally pushing
the boundary east through our region. This negatively tiled
shortwave should hang the boundary to the NW longer before rapidly
swinging it through our region late Sat into early Sun causing the
swath of heaviest rain (and possible convection given some CAPE) to
be progressive in our area. Given the possibility for some
convection and PWATs likely to exceed the maximum climatological
value of 1.25 inches, we will continue a mention of localized
flooding Fri night through Sat night in the HWO. Rain will quickly
end from W to E Sat night as the cold front moves east and drier air
filters in. Slight chance pops for a few showers will continue in NE
areas through early Sun morning.
Not much airmass change behind this system with highs in the upper
60`s to near 70 Fri and Sat only dropping to the low 60`s Sun. The
next system moves in Sun night and Mon with slight chance pops Sun
night expanding to chance to likely Mon. Temps will remain much
00Z TAF DISCUSSION.
Potent incoming system will result in widespread MVFR flight
categories tonight, with possible IFR conditions at KTRI as well.
MVFR conditions and -RA will arrive at KCHA around 08z or so,
KTYS by around 10z, and at KTRI by the 11z-12z time frame, lasting
about 4-6 hours thereafter. A fairly quick return to VFR levels
is forecast at all terminals tomorrow, with gusty west winds
accompanying the clearing. Included some IFR conditions at KTRI
around daybreak. Some -RASN could occur as the freezing level
drops within 1,500 ft AGL, but confidence not high enough to
include in the TAF at this time. Elsewhere only rain is expected.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 41 53 32 56 36 / 70 10 0 0 0
Knoxville McGhee Tyson Airport, TN 38 49 32 52 32 / 90 70 0 0 0
Oak Ridge, TN 39 49 31 52 32 / 90 60 0 0 0
Tri Cities Airport, TN 34 43 29 47 30 / 80 90 0 0 0