Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/26/18
Area Forecast Discussion
National Weather Service Green Bay WI
617 PM CST Sun Feb 25 2018
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 236 PM CST Sun Feb 25 2018
The latest RAP analysis and satellite/radar imagery show a potent
low pressure system moving northeast over northern Ontario. Low
clouds continue to wrap around the low and across northern WI,
though the light snow and flurries ended early this afternoon. A
few lower visibilities continue over north-central WI though,
due to blowing snow. Clouds have been gradually retreating
northward through the day, with most areas south of highway 29
seeing clearing skies. Winds have also gradually diminished after
peaking early this morning, and this trend should continue through
the night. Secondary wind gust max, as depicted by progged
soundings, hasnt quite materialized early this afternoon. So with
coordination from MKX, will let the advisory expire at 3 pm. As
high pressure over the Ohio Valley builds north, cloud trends is
the main forecast concern.
Tonight...As low pressure continues to lift off to northeast
Canada, high pressure centered over the Ohio Valley will gradually
build into the region. The gusty winds will continue to diminish
as the pressure gradient slackens and nocturnal cooling sets in.
Clouds will be a bit more stubborn, with an area of clouds over
the WI/MN border expected to move into central WI early this
evening. Thereafter, clouds are expected to to retreat northward
relatively quickly. Will have enough winds in the boundary layer
so decoupling is not anticipated, and so went with the best
performing guidance for lows. Temps falling into the mid- teens
north to the mid 20s south.
Monday...High pressure will continue to dominate our weather.
Under plenty of sunshine, south winds will push highs into the
upper 30s to mid 40s across the region.
.LONG TERM...Monday Night Through Sunday
Issued at 236 PM CST Sun Feb 25 2018
A weak cold front will slowly move through the forecast area on
Tuesday and Tuesday night, then slide southeast of the region
on Wednesday. The front may generate some light rain and snow
over mainly the southeast half of the forecast area Tuesday
evening, with dry conditions returning by Wednesday. Temperatures
are expected to warm well into the 40s ahead of the front on
Tuesday, then settle back into the upper 30s and lower 40s on
A sharp upper trof crossing the central Rockies will induce
cyclogenesis near the Texas/Oklahoma Panhandles during the midweek
period. This low (and the associated deepening upper trof/low)
is expected to track northeast along the stalled frontal boundary
toward Chicago/southern Lake Michigan late Wednesday night into
Thursday morning, then get shunted east through the northern Ohio
Valley. The GFS continues to be farther north with the sfc/upper
lows, and brings the potential for heavy snow into central and
east central WI (similar to the 00z ECMWF), while the 12z ECMWF
is farther south and keeps the heavy snow to our south. Surface/
925/850 mb temperatures and low-level thicknesses support mainly
snow, with some mixed precipitation in parts of east central WI
early in the event. The GFS continues to show some potential for
strong northeast to north winds, and possible Gales on Lake
Michigan Thursday and Thursday night. Will continue to mention
this system in the HWO, but with significant model differences,
will hold off on any specific details at this time.
Quiet weather is expected to return as high pressure arrives
Friday into Saturday. Precipitation may develop as the high
shifts east on Sunday. Seasonal temperatures are anticipated
over the weekend.
.AVIATION...for 00Z TAF Issuance
Issued at 555 PM CST Sun Feb 25 2018
MVFR cigs may drift over parts of north central and
central Wisconsin this evening, otherwise vfr conditions will
prevail this evening along with diminishing west to southwest
winds. VFR will continue into Monday as high pressure drifts
across the mid section of the country.
Area Forecast Discussion
National Weather Service Wilmington NC
731 PM EST Sun Feb 25 2018
A cold front will move offshore early Monday, pushing the record
warm temperatures out to sea. High pressure will build across
the central Appalachians behind the front, then will move off
the Virginia coast Tuesday night. A warm front will lift north
across the area Wednesday. Strong low pressure will push a cold
front across the area Thursday night.
.NEAR TERM /THROUGH MONDAY/...
As of 730 PM Sunday...Although the actual surface cold front is
still back across central Virginia and the mountains of North
Carolina, a prefrontal trough and wind shift has reached the
coast of the Carolinas. This boundary helped develop shallow
convection this afternoon where RAP 0-hour forecasts showed
surface-based CAPE values of 300-500 J/kg in spots. The
potential for convection has ended with the loss of daytime
heating, and in fact it looks like we`re entering a lull for
rainfall chances for the rest of the evening.
Precip chances will ramp back up from southwest to northeast
late tonight as a wave of low pressure develops across Alabama
and Georgia. Backing wind directions across the 850-700 mb
layer should begin to cause an increase in isentropic lift which
should trigger the development of rain late tonight. The bulk
of this lift should reach the area after daybreak where
measurable precipitation chances remain near 90 percent for
Changes with this forecast update include adjustments to sky
cover forecasts to show a couple hours of clearing skies this
evening, minor downward tweaks to forecast low temperatures
given this unexpected brief window for radiational cooling, and
minor edits to wind speeds and directions. Discussion from 300
Another record breaking day going down in the books for both
FLO and ILM. An 88 year old record maximum temperature broken at
ILM this afternoon by reaching 82 deg. FLO had no problem
demolishing the 79 degrees set last year, currently at 83 and
climbing. The ocean cooled air at the Myrtles is making it
difficult for CRE to reach record values this afternoon.
The pre-frontal trough crossing I-95, will merge with the sea-
breeze convergence line from 4pm-6pm, off the coast by very
early evening. Low-level winds of 20-30 kt, and a strong cap of
dry air aloft, will prevent hazardous weather this afternoon
and tonight, but gusts in stronger showers to 35 mph cannot be
ruled out entirely. Cool water and diurnal cooling will kill
this line quickly off the coast after 6 pm.
This may leave a quiet overnight period, with little forcing,
until weak upper support arrives into daybreak, and the onset of
low-level over-running gears up. The front should already be
through SE NC and NE SC by daybreak Monday, and maximums Monday,
holding below 70 in most if not all locations through the day.
Isentropic lift strengthens on Monday, co-joined with elevated
PWAT values exceeding 1.5 inches, so expecting a good little
soaking Monday. Yes there may be periods of non-rain Monday, but
latest QPF best-fit line, gives us about 1/3 inch average
across NE SC and SE NC, most of it Monday, a little more Monday
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 300 PM Sunday...Cold front to the southeast will be
moving away from the area as the period begins. Front will be
followed by surface high building in from the north. Lingering
low level moisture may lead to some areas of light rain or
drizzle for the first few hours of the period. However, cooler
and much drier air starts spreading in from the north-northeast
as early as midnight. Remainder of the period will be dry with
flat pattern aloft trending toward subtle ridging as the 5h Gulf
of Mexico ridge expands north. Forecast soundings show mid-
level subsidence starting to increase as early as daybreak Tue
and peaking in strength early Wed morning. There will be upper
level moisture moving across the top of the ridge late Tue and
Tue night, ahead of a system moving across the southern MS
Valley. This will result in increasing high clouds late Tue and
Tue night. Despite the increase in high cloud rainfall before
the end of the period is unlikely. Forecast soundings show no
appreciable moisture below 15k ft as well as strong downward
Temperatures above normal will continue through the period. Lows
each night will dip into the mid 40s for most areas. Only exception
could be Tue night in spots that typically run colder on good
radiational cooling nights. Right now it appears that increasing
high clouds Tue night will prevent strong radiational cooling, but
if clouds are slower to develop or thinner, the typical cold spots
could drop into the mid 30s. Highs Tue will be in the low to mid 60s
accompanied by abundant sunshine.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 300 PM Sunday...Wednesday looks unsettled as a warm front is
slated to lift through. However despite widespread cloud cover and
rain chances the prospects for QPF appear low due to WNW downsloping
mid level flow. On Thursday we wind up in the narrow warm sector of
the occluded system crossing the southern Great Lakes. Low level
wind fields will be rather strong so given ample sunshine some
instability should develop. Will add isolated thunder to the forecast
especially as the front looks a little faster and may arrive not
long after peak heating. Thursday night into Friday will be quite
breezy in the well-mixed CAA regime (especially Friday when
insolation will deepen the mixing). All weekend will find
cutoff/occluded cyclone well off the Delmarva. The resulting NE
surface flow will bring seasonable to slightly cool temps. Some wrap-
around moisture may make it this far south in the form of low
cloudiness from time to time.
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
As of 00Z...Terminals are VFR this evening. Showers are occurring
along a surface boundary which is currently moving offshore of KILM,
and -RA is occurring north of KLBT.
VFR expected through 11-12Z. Some patchy BR/IFR stratus is possible
overnight across the area, but will not indicate in TAFs attm
due to light patchy nature of rain today. A cold front will move
through the terminals overnight but wind speeds will remain
very light. MVFR will become more likely tomorrow morning as
rain increases. Winds will be northeast through the day, except
at KCRE/KMYR where northeast winds will become southeast by late
morning. Winds will then become northeast as a surface low
passes. By the end of the TAF period IFR cigs likely at all
terminals, except for MVFR at KFLO.
Extended Outlook...Becoming VFR overnight Mon. VFR Tue. Periods
of MVFR/SHRA Wed-Thu. VFR Fri.
NEAR TERM /THROUGH TONIGHT/...
As of 730 PM Sunday...Although the actual surface cold front
remains back across the mountains of western North Carolina
extending into central Virginia, a prefrontal trough reached the
coast late this afternoon with a shift to northwest winds.
Stronger wind speeds ended with the arrival of this trough, and
the `exercise caution` headline has been dropped. We`re in for
lighter wind speeds for the overnight period ahead of the front,
generally 10 knots or less. Isolated showers this evening may
increase in coverage late tonight as a wave of low pressure
developing across Georgia begins to pull moisture back across
the region from the south.
Changes with this update include dropping the `exercise caution`
headline, adjusting wave height forecasts downward tonight
through Monday morning, and minor adjustments to wind speed and
direction based on the latest HRRR/RAP forecast models.
Discussion from 300 PM follows...
0-20 NM are considerably more challenging than 24 hours ago, as
wind-waves have erupted across the waters, in response to
blustery SW wind. Outer water approaching 5 ft at this time, 3-4
feet inshore, and 4-5 seconds wave periods will become the
dominant energy, making for higher wave- steepness. An `Exercise
Caution` flag is flying for all waters, for 5 ft waves
offshore, and SW gusts to 20 kt common. No TSTMS expected but a
line of showers make rake the inshore waters after 6 pm,
spurring gusty and erratic winds briefly early this evening.
Winds will ease overnight as the front nears, shifting to north
in the pre-dawn hours, before daybreak all marine zones. Winds
to become perhaps E 15 KT Monday afternoon, but NE winds will
ram up notably, heading into Monday night.
SHORT TERM/MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 300 PM Sunday...Cold front will be south of the area as
the period begins with northeast surge setting up. Northeast
flow late Mon night and early Tue will be 20 to 25 kt with gusts
in excess of 30 kt likely. Surge will be of short duration but
seas building to 7 ft in the vicinity of Frying Pan Shoals are
likely. A short duration SCA will likely be needed Mon night
into Tue. Gradient starts to relax on Tue with speeds decreasing
in the afternoon. Northeast flow continues into Tue night
before the high starts to sag south, veering winds to easterly
early Wed as the center of the high slips off the NC coast. Seas
start falling late Tue afternoon and may be as low as 2 to 3 ft
by the end of the period.
LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 300 PM Sunday...Light southerly flow with a warm front
lifting through the area. Following its passage winds will turn
to SW and start increasing on Thursday. While wind speeds will
remain below thresholds it looks like some advisory-worthy 6ft
seas are possible. Cold frontal passage will lead to a sharp
turn to the NW and no appreciable decrease in wind speeds. If
anything the range of gusts may open up. Advisory may be
maintained for at least part of Friday.
Area Forecast Discussion
National Weather Service Jacksonville FL
721 PM EST Sun Feb 25 2018
.UPDATE...Radar shows a few showers ongoing from JAX area to SSI
along sea breeze and outflows...activity will gradually diminish
next few hours...then partly cloudy skies. HRRR and SREF focusing
on western half of forecast area for areas of dense fog after
midnight. Will continue areas of dense fog western counties of ne
FL...more patchy in nature further E to St. Johns River. Another
mild night with low temps in the lower-mid 60s.
.AVIATION...VFR conditions expected tonight and Mon. May have
patchy fog affect KGNV and KVQQ sites 08z-12z.
.MARINE...No changes planned in next CWF issuance.
High pressure will build SE of area early Monday. A cold front
will slide across the area waters Monday afternoon and evening.
High pressure will build to the North on Tuesday, then to the
Northeast Tuesday night, as the front lifts back to the North as
a warm front. High pressure will be to the East then Southeast
Wednesday into Wednesday night. A strong cold front is expected
to pass Southeast across the region Thursday night, with high
pressure building to the West on Friday.
Rip Currents: A low risk is expected Monday.
.PRELIMINARY POINT TEMPS/POPS...
AMG 63 78 57 70 / 20 60 30 10
SSI 64 77 60 65 / 30 30 40 10
JAX 64 83 63 71 / 20 20 30 10
SGJ 66 84 64 71 / 10 10 20 20
GNV 63 83 64 75 / 10 10 20 10
OCF 63 84 65 79 / 10 10 20 10
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
948 PM EST Sun Feb 25 2018
Issued at 945 PM EST SUN FEB 25 2018
A boundary remains stalled out to the south of the area. A mid
level disturbance is expected to interact with the boundary with at
least one sfc wave of low pressure developing and moving along
the boundary. The deepest moisture and lift should remain south
of the area later tonight and into early on Monday. The models
still vary in how far north measurable light rain will reach, but
the consensus is that the highest chance for measurable
precipitation will be along the TN and VA border counties from
Whitley and Bell through Harlan and into Letcher. Locations
further north and west will be closer to surface high pressure
gradually building into the area and should not experience more
than mid level clouds.
Some slight adjustments have been made to pops prior to 6Z or 1
AM. The latest HRRR as well as 18Z and 0Z NAM as well as 12Z and
18Z GFS guidance and radar trends suggest that light rain should
not reach the KY/TN/VA tri state area until after 6Z. Measurable
pops have generally been held to along and south of KY Highway 80
with an area of possible sprinkles in a narrow stripe further
north. Likely pops from southeast Whitley County through Bell and
into Harlan County. Rainfall there should be light, generally a
tenth of an inch or less.
.SHORT TERM...(This evening through Monday night)
Issued at 240 PM EST SUN FEB 25 2018
19z sfc analysis shows just about all of eastern Kentucky now in
the wake of a departing cold front. This front is taking the lower
clouds east along with it as high pressure bubbles in from the
west. The relaxing of the pressure gradient from this high`s
approach has lightened the winds, though they are still cold
advecting - generally from the northwest. Temperatures currently
vary from the low 50s northwest to the upper 50s southeast while
dewpoints range from low 40s west to the lower 50s in the east.
The models are in good agreement aloft through the short term
portion of the forecast. They all depict broad southwest flow
continuing over the area between strong ridging above Florida and
troughing north of the Great Lakes down to the Southern Rockies.
The tail of the northern trough will weaken and head into the Ohio
Valley later tonight into Monday morning. From this, a weakening
batch of energy and slight height falls pass through eastern
Kentucky during the day Monday. Following this, ridging and gently
rising heights will move over the area into Tuesday morning.
Given the model similarities will favor a blended solution with
an emphasis on the details from the higher resolution NAM12 and
HRRR in the near term.
Sensible weather will feature mainly just high clouds around this
evening and overnight as high pressure builds into the area.
However, one last wave along the past frontal boundary will move
through the Southern Appalachians tonight brushing far
southeastern parts of the CWA with a decent chance of rain
showers. Otherwise, all will be quiet through eastern Kentucky
with relatively mild overnight lows on tap in the upper 30s north
to mid 40s south. Monday will be a nice day under high pressure
with plenty of sunshine and temperatures climbing into the mid to
upper 50s. As the high pressure area moves east Monday night, a
night of good radiation cooling will likely set up a moderately
large ridge to valley temperature split with the hilltops in the
mid 30s and most sheltered valleys falling into the upper 20s.
Also, look for valley fog to develop late at night and possibly
be thick near the rivers and larger bodies of water.
Used the CONSShort and ShortBlend as the starting point for all
the grids through Tuesday morning. Did make some significant
changes to the valley locations for lows on Tuesday and also some
point specific temps tonight and Monday. As for PoPs, limited the
measurable rainfall to just the far southeast tonight and only for
a window of time from 06 to 12z - narrower in areal and temporal
extent than the blends.
.LONG TERM...(Tuesday through Sunday)
Issued at 316 PM EST SUN FEB 25 2018
There is good model agreement with the evolution of the mean flow
during the upcoming week and fairly good agreement with the main
weather makers for our area.
With surface high pressure slipping to our east at the start of
the forecast period, and weak upper ridging over the area, we`ll
have a warm dry day on Tuesday. On Wednesday an upper level trough
will be moving out of the southwest U.S. as a surface low develops
in the southern plains. A leading short wave trough will bring
showers to the area on Wednesday. A more significant round of
showers will occur Wednesday night into Thursday as the southern
stream trough begins interacting with some northern stream energy
and develops into a closed upper low. The associated surface low
will deepen from Wednesday into Thursday as it moves into the
northern OH Valley-southern Great Lakes area.
There is model agreement that the axis of heaviest rains from
Wednesday into Thursday will fall south of Kentucky, but the
southern part of the forecast area could still see significant
rains, especially Wednesday night into Thursday. The current
forecast calls for 1.5 to 2 inches in the southern part of the
forecast area from Wednesday into Thursday, so this will need to
be watched. It is possible some local high water issues could
develop by Thursday.
Temperatures will be well above normal for the first part of the
forecast period, but colder air will spill into the area by Friday
with more normal temperatures for the start of next weekend.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 740 PM EST SUN FEB 25 2018
VFR conditions will prevail through the period for all the TAF
sites. An increase in mid level clouds is expected from south to
north between 3Z and 9Z, though some MVFR cigs and possibly vis
is probable from 5Z to as late as 16Z or 17Z nearer to the VA and
TN borders as a surface wave passes through eastern Tennessee
tonight into early on Monday. Winds will generally be light and
variable through the period as high pressure gradually settles
over the area, especially after the surface low moves toward the
Area Forecast Discussion
National Weather Service Marquette MI
640 PM EST Sun Feb 25 2018
.SHORT TERM...(This evening through Monday)
Issued at 406 PM EST SUN FEB 25 2018
WV imagery and RAP analysis indicated a broad mid/upper level trough
through the central CONUS with and a vigorous shortwave lifting ne
through nrn Ontario to near James Bay. At the surface, a 984 mb low
was located just sw of James Bay resulting in a tight pressure
gradient through the nrn Great Lakes. w or wsw winds have gusted to
around into the 50-55 mph range at KCMX and mainly from 40-45 mph
over much of west and n cntrl Upper Michigan bringing plenty of
drifting snow. Otherwise, the cyclonic wrly flow and lingering
low level moisture has kept skies mostly cloudy over the rest of
Tonight, models suggest that the strong winds will gradually
diminish into this evening. So, the 00z wind advisory expiration
looks on track. However, winds will remain strong enough overnight
to maintain mixing with temps only falling to around 20 even with
Monday, with a transition to a more zonal patter, mild Pacific air
will spread into the region on sw low level flow WAA. Under sunny
skies, with 900 mb temps to around -3C, temps should climb into the
lower 40s over the west, toward the higher end of guidance.
.LONG TERM...(Monday night through Sunday)
Issued at 257 PM EST SUN FEB 25 2018
Overall, the weather looks to remain fairly quiet through the
extended across Upper Michigan as zonal flow dominates the upper-
level pattern through the middle of the week. Later this week, the
northern and southern streams of a longwave trough will phase across
the Middle Mississippi Valley and allow for a deepening surface
trough to track across the far lower Great Lakes region. There is
still quite a bit of uncertainty in how for north precipitation will
get with this system, but right now it looks like Upper Michigan
will be right on the edge of it. Temperatures wise, we`re not
looking at any sharp, dramatic cool downs, with temperatures
remaining mostly above normal for this time of year.
Tuesday through Wednesday: As previous mentioned, flow will remain
predominately zonal through this time period; however, a weak
shortwave will drop south Tuesday night into Wednesday pushing a weak
cold front through the region. Ahead of this front, on Tuesday
return flow will allow temperatures to warm into the 40s across much
of the area. As the front makes its way south across Upper Michigan
we could see some snow/rain showers associated with this front
across the south central and east, but this will highly depend on
how far north mid-level moisture can return prior to the arrival of
the shortwave. Behind the front, temperatures will cool down, but
with the cold air advection not being terribly impressive we`re not
looking at a sharp/dramatic cool down. As high pressure takes over
expect ample sunshine and drier weather on Wednesday.
Thursday through next weekend: As the above mentioned longwave
trough becomes better organized across the Middle Mississippi Valley
and the main surface low tracks across the lower Great Lakes region,
cloud cover will increase through the day on Thursday. Right now
uncertainties still exist in how much moisture will be able to
return this far north. Given the strength of the Hudson Bay high
during this time period and the amount of drier air being pulled
southward on the north and west side of the surface low, not
terribly excited about our precipitation changes with this system on
Thursday. Therefore, lean towards the ECMWF/Canadian solutions,
which favor a further south track for the system precipitation, and
did at least lower PoPs across the northern half of our CWA. For
collaboration sake, did opt to maintain at least chance wording
across the south half. Even if we don`t see any precipitation from
this system, the increasing pressure gradient should at least allow
for breezy conditions across much of the area.
As winds become northerly on the backside of the system Thursday
night into Friday expect lake effect clouds and perhaps some very
light wintry precipitation across the north wind snow belts. Right
now 850mb temperatures are only progged to be around -8C to -10C so
it may be a stretch to even get any snow out of the lake effect
clouds at times. On Friday, high pressure will start to dominate and
allow any lingering precipitation to come to diminish.
Next weekend upper-level ridging will dominant and allow for the dry
weather to continue. Towards the end of next weekend, another system
is progged to eject out of the intermountain west. Per usual model
solutions diverge significantly in the track/speed/timing of this
next system, especially considering it appears we may have an omega
block-like pattern slowly evolving across the CONUS. This would
favor the slower solutions, such as the ECMWF/Canadian.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 640 PM EST SUN FEB 25 2018
As low pres over James Bay continues to lift farther to the ne, MVFR
cigs at KIWD/KCMX/KSAW will lift and/or scatter out tonight. At
KCMX, IFR vis from ongoing -shsn and blsn due to winds gusting above
30kt will improve this evening as winds gradually diminish. VFR
conditions will prevail at all terminals on Mon.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 406 PM EST SUN FEB 25 2018
As low pressure continues to lift northward to James Bay westerly
gales to 45 knots with some storm force gusts will diminish this
evening and end after midnight over the east. Monday through the
middle of next week, winds in the 20 to 30 knot range early Monday
and again Monday night will gradually weaken to less than 15 knots
Wind Advisory until 7 PM EST this evening for MIZ001>005-084.
Gale Warning until 1 AM EST Monday for LSZ266-267.
Gale Warning until 10 PM EST /9 PM CST/ this evening for LSZ162-
Area Forecast Discussion
National Weather Service Blacksburg VA
918 PM EST Sun Feb 25 2018
A cold front from Lake Ontario to central Mississippi will move
southeast tonight, stalling briefly over Virginia and
Tennessee, before moving across the southeast United States on
Monday. High pressure follows the front and will over the Mid
Atlantic States on Monday night and Tuesday. A deep low pressure
system will track into the Ohio Valley on Thursday and push a
strong cold front through the area Thursday night and Friday.
.NEAR TERM /THROUGH MONDAY/...
As of 918 PM EST Sunday...
Cold front moves southeast through the region tonight into
Monday. Adjusted temperatures and pops for this evening into
tonight. Slowed the arrival time of rain in the southwest
closer to NAM and HRRR. Also, extended the north edge of rain
overnight into Monday morning. Lowered low temperatures in the
west a few degrees overnight.
As of 625 PM EST Sunday...
Made some minor adjustments in temperatures for this evening
utilizing the latest surface obs, their trends and shaped towards
GLAMP. In general, lower temperatures in the west to capture drop
this evening into tonight. Overnight low temperatures expected to be
from the mid 30s in the northwest mountains to lower 50s in
piedmont. More adjustments later tonight.
As of 300 PM EST Sunday...
500MB flow remains southwest tonight and Monday which will
limit/slow down southern advance of cooler and drier air. Southwest
Virginia, southeast West Virginia, and northwest North Carolina stay
in broad upper diffluence until Monday afternoon. At the same time
weak pieces of short wave energy track through the area from the
southwest. 12km NAM showed good insentropic lift tonight in the 800-
600MB layer over southern Virginia and northern North Carolina,
especially after midnight.
The surface front extended from near Pittsburgh to Nashville this
afternoon. The surface and 850 MB front stall around the
Virginia/North Carolina border this evening, then slowly move south
throughout the day Monday. Winds turn to the northwest and north
Monday behind the front. Areal coverage of showers will continue to
diminish this afternoon, then fill back in between 00Z/7PM and
06Z/1AM. SOme differences in the guidance with northern extent of
precipitation, with the NAM and HRRR as far north as Lewisburg and
Clouds and precipitation Monday morning will hold back on
heating and with much of the region on the north side of the front,
plan on lowering maximum temperatures.
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 310 PM EST Sunday...
Surface cold front hanging around just south of the NC border on
Monday then shifts southward essentially as a wedge front early
Monday evening. This will lead to rapid clearing and drying as large
surface ridge associated with cooler low-level air mass than
experienced recently builds into the VA Highlands into central WV.
Good radiational cooling and 850mb temperatures within a couple
degrees of zero supports lows in the upper 20s to middle/upper 30s.
Will still need to watch for overnight mist or fog with radiation
inversion setting in, winds trending calm, and wet ground from a
couple days worth of rain, though confidence isn`t high enough to
place in the forecast.
Quiet and rather pleasant Tuesday on tap as high pressure progresses
east late in the day, though a bit cooler temps in the 50s than
experienced recently. Tuesday night will feature clear skies
initially, but then increased isentropic lift from the southwest
will force greater/lowering cloud cover ahead of a warm front. Will
show limited chances for rain - slight/low chance - mostly west of I-
77 into the pre-dawn Wednesday hours, but best chance of rain is
Wednesday. Timing of the cloud cover suggests that areas north/east
of I-77 stands a fair shot at seeing lows around sunrise, and
somewhat earlier on the other side of I-77.
Elongated west-east warm front, associated with a potent southern-
stream shortwave trough way back into the southern Rockies/Plains
region, then begins to spread northward. I say begin, because unlike
yesterday, it`s not clear in the 12z NWP suite exactly how far north
the warm front gets. The NAM`s position is the southern outlier -
roughly along I-40 in NC - while the GFS is the furthest northeast,
closer to the Route 460 corridor. The ECMWF and GEM are somewhere in
between. Model-generated QPF also falls on the cooler side of the
frontal zone, which if is the case would favor a slower frontal
position. All that said, did opt to sharpen PoPs/QPF some across the
forecast area Wed/Wed night, showing Likely to Categorical from
roughly give-or-take southwest of the Roanoke River with better
proximity to the warm front, with chance north. It`s not until
the after-midnight period when it`s generally agreed upon that
the warm front begins to move northward where the best chance of
rain areawide occurs.
Regardless, this is likely to be the start of a rather active
period, with warm-frontal QPF values between a quarter to three-
quarters of an inch, wetter further south. More will fall on
Thursday. In terms of temps, undercut MOS by several degrees on
the highs - only showing 50s areawide with overcast skies and
rain ahead of the warm front. Also left lows falling maybe a
couple degrees from daytime highs with the best push of warm
advection overnight and continued clouds/rain.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 310 PM EST Sunday...
Though there are still some rather significant details to pin down
mostly on the mesoscale, confidence continues to increase that
Thursday and part of Friday should be an active period of weather.
In mid-levels a powerful southern-stream trough phases with northern-
stream energy, evolving into a closed off upper low Thursday that
makes slow east progress.
Initial surface low in the central Plains Wednesday night moves
northward and looks to occlude, while a secondary low then
develops along the warm front in the Tennessee Valley and moves
northeast across the central Appalachians into New England
Thursday-Thursday night. This should bring warm sector rains to
the region on Thursday, infused by PWAT values between
1.25-1.5". Depending on how quickly we can get into the warm
sector will determine if thunder is possible for parts of or all
of the region Thursday, but there is strong diffluence aloft
indicated in the global models as well as rather strong vertical
wind shear. Since it`ll likely be raining Wednesday into
Thursday, did take a look at the MMEFS for some of our river
gages, and based on NAEFS and GEFS QPF input they do show some
conditional rises on some of the rivers between Thursday and
Northwest winds also appear to become at least quite breezy
Thursday night into Friday. 12z MEX-based MOS wind speeds for
many of our MOS forecast points are between 30 and 38 knots, a
pretty impressive signal considering it is still Day- 5/Day-6.
Did raise wind speeds up Thursday night-Friday based on those
MOS signals and favorable pressure rises. Nonetheless, will need
to continue to carefully monitor the late-week period.
Temperatures will also begin to cool towards more seasonal
levels Friday into the weekend.
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
As of 630 PM EST Monday...
Cold front continue moving southeast this evening becoming
stalled near the Virginia/ North Carolina border tonight.
Scattered light MVFR showers are possible along the front but
overall conditions remained VFR.
Rain fill back in over southern Virginia and northern North
Carolina tonight, mainly after 03Z/10PM as a low tracks along
the front. High confidence of widespread MVFR to IFR ceilings in
the foothills and mountains after midnight. Winds turn to the
northwest and north behind the front. Lower confidence how
extensive fog will be tonight and Monday morning. Expecting MVFR
fog where there is rain. MVFR to IFR conditions will continue
for Monday morning. Light northerly winds are expected for
Confidence is medium on cigs/vsbys/winds through the fcst pd.
Sub-VFR conditions may extend through Monday night as the front
sinks south. High pressure builds over the region into Tuesday
which should bring drier conditions and VFR, at least
temporarily. By late Wednesday into Thursday rain and MVFR to
IFR ceilings will return to the region. A strong cold front
crosses the region Thursday night with much colder air and strong
gusty winds behind the front Thursday night and Friday.
Area Forecast Discussion
National Weather Service Shreveport LA
926 PM CST Sun Feb 25 2018
Strong positively tilted upper level trough axis is currently
residing across Eastern Kansas and pulling out of the OK/TX Pnhdl
region of the country late this evening. Lift in association with
this trough axis is confined to our southern and eastern zones, in
association with the large rain shield across these same
locations. The back edge of this rain shield continues to make
slow but steady progress eastward across the Lower Toledo Bend
Country of Deep East Texas into portions of Central and Northeast
Louisiana. Extrapolating the eastward progression of this rain
shield over time puts the back edge of rain only across our
extreme southeast parishes near or shortly after midnight. With
drier mid level air rapidly infiltrating our region from the west
with the arrival of the trough, have removed pops for the
remainder of the night for all but our southeast third where pops
are still categorical in nature.
Satellite imagery via the GOES 16 Nighttime Microphysics Channel
shows the clearing line of cloud cover trying to move further
towards the Interstate 30 Corridor of Northeast Texas into
Southwest Arkansas but I`m having my doubts about just how much
further south and east the clearing line will make it. In fact,
00z progs have this cloud cover possibly beginning to retrograde
back to the north and west overnight. Also getting a little
concerned with the development of fog overnight across our
southern and western most zones with the latest HRRR output
showing this possibility the best. For this reason, have added fog
to the grids across our southern and western most zones.
Other changes included hourly temp/dewpoint and sky grids to mimic
current and forecast hourly changes.
Update out shortly...13.
.PREV DISCUSSION... /issued 616 PM CST Sun Feb 25 2018/
For the ArkLaTex, IFR for KLFK with MVFR/VFR everywhere else as a
large area of showers extends from KLFK to near KELD and points
SE. This area of showers will continue to move E this evening and
should push E of KMLU by 06Z. Light NE winds will keep cigs/vsby
issues IFR, but skies should lift and clear from NE to SE 12Z-
18Z. Climb winds are NE only to about 2kft and quickly veer to SE
then SW by 4kft. Speeds increase from 20-80KT into flight levels.
Outlook is for dry weather for Monday and half of Tuesday.
.PRELIMINARY POINT TEMPS/POPS...
SHV 45 69 50 68 / 10 10 10 70
MLU 48 69 47 70 / 90 10 10 60
DEQ 41 68 43 64 / 10 0 10 60
TXK 43 68 46 65 / 10 10 10 70
ELD 43 69 44 67 / 10 10 10 60
TYR 49 70 50 67 / 10 10 10 70
GGG 47 70 50 67 / 10 10 10 70
LFK 51 72 54 72 / 20 10 10 70