Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/18/23
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
901 PM CDT Tue Oct 17 2023
.UPDATE...
Issued at 850 PM CDT Tue Oct 17 2023
Watching progression of the cold front as it marches eastward,
currently passing through KMBG as of this writing. Been seeing
gusts over 50 or even 55 mph (KMBG), but based on upstream
activity, the strongest of winds seem fairly brief - maybe an hour
or less. HRRR continues to show potential for advisory criteria
speeds through around 04Z/05Z, but maybe harder to achieve as we
begin our nocturnal inversion. RAP Bufkit soundings generally show
this idea, with maybe some mix down potential still in KMBG, but
maybe a bit harder once you get to the southern CWA in a couple
hours. That said, still feel gusts over 45 mph seem somewhat
likely, albeit probably short lived. Issued a short Wind Advisory
for collaboration purposes with FSD to account for the high gust
potential still over the next couple hours. Otherwise, will make
some fine tuning to other wx elements (including PoPs) through the
night, but forecast is generally in good shape already.
&&
.SHORT TERM...(This Evening through Wednesday Night)
Issued at 143 PM CDT Tue Oct 17 2023
Key Messages:
- 25-55% chance of showers over the next 24 hours, primarily
during the day on Wednesday.
- Gusty northwest winds are expected in two phases tonight and
Wednesday. The first phase is associated with showers this
evening over central SD and could produce wind gusts of 40-55mph
in central SD. The second phase is again over central SD during
the day Wednesday, with gusts of 35-45mph.
Main focus for the next 24hrs will be tied to the shortwave spinning
along the MT/Alberta/Saskatchewan border at this time, with a 998mb
surface low located in central Saskatchewan. Both features will be
dropping southeast across the Northern Plains over the next 24-
30hrs, leading to winds gusting to the 30-45mph range at times,
along with scattered showers (25-55%). Currently, clear skies cover
the eastern portions of the CWA, while high clouds are overspreading
central SD ahead of the approaching system. Ahead of the surface
trough in the western Dakotas, south-southeast winds have increased
over eastern SD and leading to gusts around 20kts. With mixing up to
925-900mb this afternoon (around 14-17C at that level), have seen
temps rise into the 60s and lower 70s thus far. With drier low
levels in place, will likely be tough for this initial wave of
clouds to produce precipitation along the ND/SD border late this
afternoon and into the evening, but continue to get hints of that in
the CAMs model reflectivity (best moisture/forcing between 650-
450mb). But when looking at the accumulated precip, there isn`t much
indicated, so may end up being more of a sprinkle or virga. That
said, did include some slight chance PoPs into the first part of the
evening into northeast SD, where models indicate the best
forcing/moisture/reflectivity.
The initial precipitation with the cold front and leading shortwave
energy will arrive between 02-04Z around Corson/Dewey/Stanley
counties. CAMs fairly consistent with this idea, but vary in the
intensity of the showers. HRRR is one of the stronger CAMs and is
showing some weak lightning rates. Deterministic ECMWF also showing
lightning with the cold front showers, but keeps it in western/swrn
SD. Overall, the instability is really lacking (tough to find much,
if anything, above 100 J/kg of MUCAPE in northwest SD), so lightning
potential is limited and have left out for now. The primary concern
with the showers will be increasing downward motion from rain
entering the dry sub-cloud layer and combining with the area of
pressure rises along/behind the front. This could lead to a brief
period of winds gusting to 40-55mph with the showers over central
SD. HRRR has been consistent in that idea with each run from 09Z-17Z
this morning, including showing gusts up above 50mph as it moves
into Corson/Dewey/Stanley counties. As mentioned above, the HRRR is
definitely on the stronger side of the solutions, but even some of
the weaker CAMs, including the HopWRF runs, are showing gusts to
that range immediately behind the front and with weak showers. With
the short duration and more convective type of setup, think this
could be best captured with SPS products as it moves through the
area this evening.
Behind the initial showers with the front, will get a short couple
hour period of mid level drying before better/deeper moisture
associated with the shortwave moves into the area. This will produce
the scattered showers (25-55%) around day break and into Wednesday
evening. Expect the initial area to be over central/north-central SD
tomorrow morning, then focus along/east of the James River valley
heading into the afternoon (aided by secondary trough rotating
around the low). Overall, amounts look to be limited and staying
below 0.15" (75th percentile for the event). Main shortwave energy
is largely through the CWA by 00Z Thursday, as it continues to the
southeast. Thus, expect a diminishing trend to the showers from west
to east in the late afternoon and evening and done by around
midnight.
Finally, for the wind side of things, it`s going to come in two
phases. The first phase is the previously mentioned showers and
associated strong winds in the evening. After that moves through, we
lose the better pressure rises behind the front and there`s limited
cold air advection, so most deterministic/ensemble models are
showing the nocturnal inversion taking hold and likely limiting the
gusts through the overnight hours. Did continue to trend down from
the NBM and towards the new experimental NBM v4.2 winds, as those
have shown superior performance in events like this at night. But as
diurnal mixing increases on Wednesday morning, expect winds to
increase across the area, with the greatest winds in the morning
over the central SD, where winds at the top of the mixed layer (900-
850mb) are around 40-45kts. Again, lacking pressure rises and cold
air advection, so may not fully realize the top of the mixed layer,
but mean momentum transfer winds are in the mid 30kts and expect
occasional higher gusts. ECMWF-Ens EFI data in the 0.7-0.8 range
over central SD for the 24hr range from 00Z 18th to 00Z 19th, which
is similar to past events that were right around wind advisory
levels. The strongest winds are expected to around 18-21Z in central
SD, as high pressure will move eastward into western SD in the
afternoon and steadily decrease winds aloft. Elsewhere, expect
northwesterly gusts over northeast SD in the 25-35 mph range and
diminishing in the evening as diurnal mixing is lost.
.LONG TERM...(Thursday through Tuesday)
Issued at 143 PM CDT Tue Oct 17 2023
KEY MESSAGES:
- Dry conditons for the end of the week through the weekend with
temperatures above average.
Clusters are in solid agreement with a ridging pattern over the
western CONUS and a trough over the eastern CONUS for the end of the
week along with a shortwave/low riding over and down the ridge, from
Canada into MN (moisture stays east of CWA). NAEFS indicates this
ridge`s height at 200mb is 99.5% above climo norm! This continues to
be the main pattern through the weekend with the ridge pushing
slightly east. With this pattern, the Northern Plains will remain in
northwest flow aloft. Early next week, ensembles are still in pretty
solid agreement with the ridge over central and Northern Plains as
another trough moves onshore over the western CONUS. Slight
variation in timing and heights of this ridge and incoming trough.
By the middle of next week, we will flip flop with the trough over
the western CONUS and ridge over the eastern CONUS. With this setup,
no moisture is expected through the weekend per deterministic and
ensembles. Models/NBM hint that Tuesday/Wednesday, as this trough
moves east (and surface features), could be our next chance of
precip in the form of rain. Confidence remains low at this time on
timing/intensity as this is several days out.
Above average temps at 850mb will lead to 2m highs, Thursday and
Friday, in the 60s and 70s. With a high pressure system moving in
Saturday, highs will be a few degrees cooler but still above
average. Sunday into early next week with be around average to
slightly above average. Winds look to be gusty out of the northwest
Friday afternoon, along with dry conditions, which may lead to a
fire concerns in central and west central SD.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 651 PM CDT Tue Oct 17 2023
Terminals KABR,KATY,KPIR,KMBG
A strong frontal boundary will move east across the region this
evening, switching winds around to the northwest with gusts over
30 knots likely. They will first arrive in KPIR/KMBG towards the
start of the TAF period, then over to KABR/KATY (with lesser
speeds) later this evening. MVFR CIGs are forecast to arrive by
early morning as well, which are included in the TAFs. -SHRA also
expected at times as this whole system moves through.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until midnight CDT /11 PM MDT/ tonight for SDZ003-
004-009-015-016-033>036-045-048-051.
MN...None.
&&
$$
UPDATE...TMT
SHORT TERM...SRF
LONG TERM...MMM
AVIATION...TMT
Area Forecast Discussion
National Weather Service La Crosse WI
1054 PM CDT Tue Oct 17 2023
.DISCUSSION...(This evening through Tuesday)
Issued at 154 PM CDT Tue Oct 17 2023
Key Messages:
- Scattered light showers expected to move through Wednesday into
Thursday (40 to 60% chance) with amounts generally around 1/10
inch or less.
- Additional light rain possible on Friday mainly east of
Mississippi River
Incoming Rain Chances on Wednesday:
GOES Water vapor imagery showing the next weather system for the
area currently over southern Alberta with an impressive circulation.
Rain showers are primarily just ahead of the mid-level circulation
across southern Alberta, otherwise observations show 10-12kft clouds
and sprinkles in ern MT and wrn ND. Surface pressures were falling
across all of the High Plains with a surface low center west of
KBIS. Southerly flow ahead of the low will keep overnight
temperatures warmer tonight with mainly high cirrus increasing.
Should enough low-level cooling in the boundary layer, some stratus
may form north of I-90 overnight, dissipating as warming aloft
occurs toward sunrise.
The overwhelming notable forecast challenge with this system is
the very dry air mass in place with forcing increasing. The latest
trends are to track the mid-level low further southwest through
northeast IA. Warm advection in the low-levels and increasing QG-
induced lift will be spent saturating the dry air mass. The cold
front traverses the area slowly Wednesday, becoming nearly
stationary in central WI, as the mid-level low shifts southwest of
the area. This will provide low-level convergence to try and
saturate below 10kft during the afternoon. The most saturated
forecast soundings are near the front in central WI in the
afternoon hours where diurnal heating can add a boost as
temperatures cool aloft. 17.12Z HREF probabilities are about 60%
for 0.10"+ near and north of the I-94 corridor Wed afternoon,
ramping up eastward. Have followed this idea with rain chances
falling drastically into northeast IA /20%/..with just too much
dry air to overcome in the daytime. There is a morsel of elevated
instability that could shower from 10kft briefly pre-frontal
Wednesday morning. Those who do see rain, it will be minor, less
than 0.10" (70% chance in the HREF). Periods of clouds and
sprinkles southwest of I-94 seems to describe Wed.
Additional Hit or Miss Rain Chances Through Late Week:
The upper low will pass overhead Wednesday evening with
deterministic guidance showing some variance in its exact track.
Canadian and RAP are the southernmost solutions, taking it by just
south of our forecast area. Looking at ensemble means, there has
been a trend favoring a more southward shift the last few runs. This
is most evident in GEFS and CMC guidance. QG forcing around the low
will support continued chances for wrap-around showers into
Wednesday night, aided by more favorably saturated low levels as
seen in forecast soundings. If the low track continues to trend
southward, the main focus for wrap around showers may end up being
more to the south of our area Wednesday night, though scattered
light showers or some drizzle would still be a possibility.
Additional light rain Wednesday night should amount to less than
1/10 inch for most per latest CAMs and HREF.
As the low pulls away on Thursday with the more favorable forcing
and moisture, any additional light wrap-around showers should stay
mainly east of the Mississippi River. But hot on the heels of this
departing system, a progressive shortwave within the cyclonic flow
aloft will dive through the area on Friday. Models diverge on speed
and intensity of this feature, with NAM and Canadian being the
faster solutions while ECMWF develops a deeper wave and GFS has a
slower, weak wave. Highest probabilities (30%) for additional light
rain remain mainly east of the Mississippi River.
Depending on how quickly this shortwave exits the area, the weekend
is shaping up to look dry and seasonable for most. Broad ridging
over the western CONUS should bring gradual height rises into the
region with what looks to be low-amplitude ridging overhead for
early next week. This should bring somewhat warmer temperatures,
likely above normal.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1055 PM CDT Tue Oct 17 2023
A shortwave trough over the western Dakotas will move southeast
toward the area overnight and Wednesday, and then move slowly
through the Upper Mississippi River Valley on Wednesday night and
Thursday. Warm air advection ahead of this system will produce
showers at the TAF sites from late Wednesday morning into the
afternoon. Ceilings will gradually lower and possibly become MVFR
on Wednesday evening.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
DISCUSSION...Baumgardt/Kurz
AVIATION...Boyne
Area Forecast Discussion
National Weather Service Cleveland OH
945 PM EDT Tue Oct 17 2023
.SYNOPSIS...
Surface high pressure builds across the East Coast through
Wednesday night. Low pressure over the northern Great Lakes will
lift a warm front eastward across the lower Great Lakes on
Thursday. This low will swing a cold front across the area
Thursday night into Friday.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
Temperatures are dropping quickly in NW Ohio where skies have
cleared and winds are light. The cloud forecast remains tricky
as clouds try to clear from the west while also seeing some
expansion of cloud across Indiana that will fill in across the
Toledo area after midnight and attempt to catch up to the
remaining cloud deck to the east. With that said, lowered
temperatures in NW Ohio where several hours of clear or partly
cloudy skies are expected. Could see a couple sites in our
southwestern tier of counties creep down towards the mid 30s
but think the duration will be short enough that we won`t see a
lot of frost form.
Previous discussion...Continued drying in the low levels this
afternoon and evening will allow for lake enhanced rain
showers/drizzle to gradually exit the forecast area. Mean layer
flow turns southwesterly and will push any remaining lake effect
rain showers over Lake Erie and into western New York by
tonight. Mild and quiet on Wednesday with peaks of sunshine as
mid-level ridging and high pressure continue to build into the
Ohio Valley. Low pressure centered over the northern Great Lakes
will lift a warm front across the lower Great Lakes region
Wednesday night. Cloud cover and shower chances will increase
from west to east as the warm front lifts eastward.
Overnight lows tonight settle near average in the lower 40s with
cloud cover gradually diminishing. Anticipate near average highs
areawide on Wednesday in the lower 60s. Warm air advection Wednesday
evening as the front lifts will lead to warmer than normal overnight
lows in the lower 50s.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
At the start of the short term period, an upper level trough will
begin to push towards the area as a surface low meanders across the
western Great Lakes. As this low pivots, an area of enhanced upper
level divergence and vorticity will allow for showers to begin to
develop ahead of an approaching cold front. Although the area will
technically be in the warm sector of the low on Thursday, the
widespread precipitation will keep things cooler with highs climbing
into the low to mid 60s. In addition, a sustained southwest flow
will become enhanced as a LLJ of 35-45 knots is mixed down to the
surface. As a result, winds late Thursday morning through the
evening will be sustained at 20-25 mph, gusting up to 30 mph,
especially for areas west of I71. Showers are expected to continue
Thursday night with lows dropping into the low 50s.
On Friday morning, the aforementioned cold front will finally push
east across the area as the trough axis shifts east of the area. As
the front pushes east, winds will back and become northwesterly at 5-
10 mph, possibly up to 15 mph for far northwest Ohio. This will mark
the transition back to a CAA regime across the region. Post-frontal
showers are expected to continue through Friday, although the
chances will gradually lower for western counties late Friday.
Chance of rainfall will remain high over NE OH and NW PA as some
lake enhancement is expected to help maintain the showers over that
portion of the area. Although it will be chilly, all precipitation
is expected to remain liquid. Highs on Friday will climb into the
mid to upper 50s, cooling overnight into the mid 40s.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
The aforementioned deepening trough and subsequent shortwave troughs
will continue to impact the area through the remainder of this
forecast period. Long range models are fairly consistent in these
features occurring and the timing of them, but the biggest
difference is the overall strength of the trough. On Saturday, a
surface low dives southeast across the CWA, bringing another
enhanced area of support for continued showers through Saturday
evening. Opted to keep the highest PoPs in the typical snowbelt
areas during this initial time with chance PoPs elsewhere with some
uncertainty amongst models. With the CAA expected to strengthen,
there should be increased lake induced instability to support lake
enhanced rain showers over these areas, which will likely continue
through much of Sunday before much drier air builds in with a high
pressure system and approaching upper level ridge. Exact timing of
the development of this high diverges amongst models a bit, so opted
to end all showers by Monday morning.
High temperatures for much of the long term period will climb into
the 50s, possibly touching 60 by Tuesday. Overnight lows will be the
bigger story as CAA allows temperatures to fall into the upper 30s
to low 40s on Saturday. On Sunday and Monday nights, decreased cloud
cover from the higher pressure system will result in enhanced
diurnal cooling which will likely result in temperatures falling
into the 30s for much of the area. With winds calming a bit over
these two night, wouldn`t be surprised if there was widespread frost
across the area.
&&
.AVIATION /00Z Wednesday THROUGH Sunday/...
A stratus deck remains at all but the I-75 corridor terminals
this evening. While some clearing is forecast to move eastward,
we are also seeing some cloud re-develop near 4-5K feet across
western Michigan and northern Indiana. The RAP and NAM indicate
clouds will fill back in across northwest and north central
Ohio by morning with eastern terminals holding onto clouds
through midday Wednesday. Trended the TAFs a little more
pessimistic with longer duration of bkn-ovc conditions although
primarily VFR. Some MVFR is possible, especially after 10Z but
confidence is not high in determining between a 3 or 4K deck.
Southwest flow should increase and help to scatter clouds out
between 15-20Z, leaving a thickening high cloud deck in the
afternoon.
Light south to southwest winds will be 5 knots or less
overnight, increasing into the 5-10 knot range after 12Z
Wednesday.
Outlook...Non-VFR expected in rain showers and/or low ceilings Thursday
through Saturday.
&&
.MARINE...
High pressure has become established over the area, allowing winds
to become west-southwest at 10-15 knots. On Wednesday, a deepening
trough is expected to begin to push south across the central U.S.
with a surface low centered over the upper Midwest. This is expected
to begin to increase the pressure gradient across the area, allowing
winds to strengthen to 15-20 knots from the south by Wednesday
night. By Thursday morning, a warm front will lift north of the Lake
and winds are expected to continue to strengthen to 15-20 knots for
the western and eastern basins, approaching 25 knots across the
central basin. Although the near shore waters should remain below 20
knots and with a sustained offshore flow, this period on Thursday
through Thursday night will need to monitored for potential marine
headlines.
On Friday morning, a cold front will push east across Lake Erie as
the associated low moves into New England. This will shift winds to
the northwest at 10-15 knots with waves up to 3 feet. This low is
expected to strengthen over New England, increasing the pressure
gradient again over the area. This will result in winds increasing
to 15-20 knots. With this sustained direction and speed, waves will
likely build over 4 feet and mark another period that a Small Craft
Advisory may be needed. These condition will continue through much
of Sunday before a surface high pressure builds over the area and
allow winds to gradually weaken.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.
&&
$$
SYNOPSIS...Iverson
NEAR TERM...KEC/Iverson
SHORT TERM...Campbell
LONG TERM...Campbell
AVIATION...KEC
MARINE...Campbell
Area Forecast Discussion
National Weather Service Dodge City KS
552 PM CDT Tue Oct 17 2023
...Updated aviation section...
.SHORT TERM...(This evening through Wednesday night)
Issued at 300 PM CDT Tue Oct 17 2023
.KEY MESSAGES...
- Strong Gusty Winds (gusts as high as 35 to 45 mph)
developing around start of the school-day/workday Wednesday
morning which could damage outdoor items and result in hazardous
driving conditions for high profile vehicles.
- Windy conditions will help create elevated fire weather risk
(Relative humidity as low as 25% and gusty winds in excess of 30
mph) Wednesday afternoon.
HRRR models shows a light wind field continuing through the late
afternoon and evening as wind directions shift more out of the
southeast this early evening and then from the southeast after
sunset. Cirrus should increase in waves in advance of a developing
Northern Plains system, that will drive a cold front into Kansas
early Wednesday.
The most impactful weather element in the short term will be the
winds early Wednesday. A cold front will be driven southeast into
the region overnight, abruptly turning winds out of the north then
northeast with time from about 6 through 10 am (Scott City - to
Medicine Lodge, respectively) and bringing the greatest potential
for strongest gusts as high as around 45 mph briefly in the post
sunrise hours. Sustained wind speeds behind the front could be as
high as 25 to 30 mph based on the Short Range Ensemble ARW and NMB
members. High confidence exists with respect to a windy morning,
with also high confidence (80%) that the winds will lose momentum
in the afternoon, with generally much lighter winds in the evening
around Elkhart and Garden city, and still gradually weakening 10
- 15 mph winds in the central Kansas counties (Hays, for example).
.LONG TERM...(Thursday through Tuesday)
Issued at 300 PM CDT Tue Oct 17 2023
.KEY MESSAGE...
The pattern will be in a shift from an upper troughing to ridging
on the broader synoptic scale, with a return to dry westerly
downsloping winds Thursday and Friday and becoming more variable
by the weekend. This is anticipated to be a period of no
precipitation, with slight chance probabilities of precipitation
(15-30%) returning to the NBM (National Blend of Models) by the
early part of Tuesday, as the overall synoptic pattern completely
shifts to an approaching upper trough once again. Warmest
temperatures in the time window could be on Friday when the NBM
75th percentile points to widespread upper 80s from Hays to the
Panhandles.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 546 PM CDT Tue Oct 17 2023
VFR conditions will prevail through tomorrow with some mid level
clouds along a cold front tomorrow. Winds will start out from a
southerly direction this evening, curling to the north by late
morning tomorrow. Wind speeds over 20 knots will be felt behind
this cold front decreasing in intensity tomorrow evening.
&&
.FIRE WEATHER...
Issued at 233 PM CDT Tue Oct 17 2023
For Wednesday , HREF combined probabilities for relative humidity
less than 25% and wind speeds in excess of 15 mph are greatest
(90%) behind the front Wednesday afternoon and in a broad arc from
around Scott City to Lakin region, southeast across Garden City
and Dodge City. In this region, low humidity and windy conditions
will lead to dangerous fire conditions where fires can escape
control more easily and be difficult to contain.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 49 76 43 81 / 0 0 0 0
GCK 47 74 40 80 / 0 0 0 0
EHA 48 74 43 82 / 0 0 0 0
LBL 45 75 41 82 / 0 0 0 0
HYS 50 74 43 79 / 0 0 0 0
P28 48 78 46 81 / 0 0 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Hovorka_42
LONG TERM...Hovorka_42
AVIATION...Hovorka_42
FIRE WEATHER...Hovorka_42
Area Forecast Discussion
National Weather Service Morristown TN
917 PM EDT Tue Oct 17 2023
...New UPDATE...
.UPDATE...
Issued at 912 PM EDT Tue Oct 17 2023
Not a lot of change from the previous forecast. The main
complication overnight is still dealing with how quickly clouds
erode. There is still a significant amount of cloud cover along
I-40 and northward. However, if you loop the past few hours worth
of satellite data clearing is evident, just slow. Latest runs of
the HRRR support further clearing through the night which is still
in line with the forecast. So still a chance for some patchy fog
and/or frost for some areas if clearing can happen early enough.
Only changes to forecast were adjusting hourly temps and
dewpoints, as our northern areas are running a little warmer due
to current cloud cover.
&&
.SHORT TERM...
(This evening through Wednesday)
Issued at 327 PM EDT Tue Oct 17 2023
Key Messages:
1. Dry weather through the period, with a warming trend for
Wednesday.
2. Very patchy frost possible in sheltered valleys of far NE TN and
SW VA tonight, as well as in higher elevations of the East
Tennessee mountains.
Discussion:
On the synoptic scale, deep northwesterly flow remains in place
across the region as upper level troughing continues to slowly
meander eastward and surface high pressure builds in from the west.
Visible satellite trends depict this afternoons pesky clouds are
finally showing signs of slowly clearing out in southern portions of
the East Tennessee valley, however, they continue to linger in
central and northern portions, as well as across higher elevations.
Unfortunately model guidance has been handling this cloud cover
poorly as they generally clear clouds out much quicker than what has
been observed. For example, by ECMWF thoughts - the skies should be
perfectly clear at the time of this discussion. As such, there
remains uncertainty as to how these clouds will play out but have
opted to trend sky cover towards more aggressive models such as the
NAMdmg, NBM90th, and ADJMET. Have also blended slightly cooler
temperatures over the next few hours given the lack of solar heating
due to these clouds.
How quick and to what extent the clouds clear out tonight will
impact the potential for patchy fog and patchy frost in sheltered
valleys and higher elevations overnight. Current forecast depicts
clouds eventually diminishing around 2-3z timeframe allowing for
decent radiational cooling to take place, favoring the scenario of
very patchy frost in sheltered valleys of far NE TN, SW VA, and
higher elevations. If the trend of models struggling with clouds
persists over the next 12-16 hours, overnight lows may be a couple
degrees low, in which case patchy frost would be unlikely. Either
way, rather unimpactful weather tonight. Much more sunshine
tomorrow afternoon as troughing lifts further eastward and H5
heights increase from 568dam to 576dam locally. Temperatures will
be around 10 degrees warmer.
&&
.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 327 PM EDT Tue Oct 17 2023
Key Messages:
1. Widespread showers will move across the area Thursday night
through Friday.
2. Orographic northwest flow rain showers expected across the
mountains for Friday night and parts of Saturday.
3. Dry and mild weather for Sunday into early next week.
Discussion:
Wednesday night into early Thursday looks to remain dry as high
pressure continues to exert influence. However, a strong upper
trough and cutoff low will be digging southeast across the
Midwestern states during this time. Further deepening is forecast on
Thursday into Friday as a strong Pacific jet extends southeast out
of Canada into the upstream side of this trough over the northern
plains.
For most locations, Thursday will be dry as the trough and
associated cold front will be too far west to produce rainfall over
our CWA I think. Will see the low level wind field strengthen
however, with breezy conditions expected for most areas during the
day Thu, especially over the northern plateau. Lack of strong CAD
east of the Appalachians, along with unfavorable southwesterly H85
wind direction doesn`t indicate there will be much of any mountain
wave action but I`m sure some of the ridge and mountain tops in the
Smokies will be windy. Rainfall begins to overspread the forecast
area from the west Thursday night and continues into the daytime
hours on Friday. Soundings indicate that some meager instability
will be present ahead of the front, so could see a few rumbles of
thunder being possible. Doubt there will be a ton however, as the
CAPE values are less than 500 J/kg, and there`s still uncertainty
with respect to how much rain coverage we`re going to have.
Trough shifts east of us by Friday evening, transitioning any
remaining precipitation to northwest flow showers confined mainly to
the higher terrain of the Smokies northward into Virginia. Models
show this northwesterly flow pattern and possible high terrain
showers continuing well into the weekend, with another potent
shortwave moving through West Virginia late Sat night to finally
wrap it up.
For Sunday into early next week, upper trough lifts northeast with
drier air and eventually upper ridging developing over the Tennessee
valley. Milder and drier conditions are anticipated especially by
early next week.
&&
.AVIATION...
(00Z TAFS)
Issued at 721 PM EDT Tue Oct 17 2023
VFR conditions at CHA through the period. Widespread cloud cover
still affecting TYS and TRI. Hi-res models not handling current
clouds very well. Therefore, low confidence forecast in terms of
fog potential at TYS and TRI overnight. If clouds clear early
enough, TEMPO MVFR fog at TRI. If clouds persist through most of
the night, then likely no fog. Otherwise, VFR through the period.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 44 71 49 71 / 0 0 0 10
Knoxville McGhee Tyson Airport, TN 41 69 47 70 / 0 0 0 10
Oak Ridge, TN 42 68 47 69 / 0 0 0 20
Tri Cities Airport, TN 39 66 43 68 / 0 0 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...
LONG TERM....CD
AVIATION...