Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/10/18

Area Forecast Discussion

National Weather Service Charleston SC

 1034 PM EST Fri Feb 9 2018

.SYNOPSIS...
A warm front will lift across the region tonight. This weekend,
a cold front will slowly approach southeast Georgia and South
Carolina from the northwest, moving and stalling near the coast
late Monday night into Tuesday. Weak high pressure expected to
build over the region by mid week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Rains were tapering off across the Charleston Tri-county area
as the 925 MB warm front presses northward. Warm and moist air
in the boundary layer will stream atop the slightly cooler and
saturated near-surface air mass and this was already resulting
in widespread expansion of stratus clouds which should lower
overnight. The stratus build-down looks most promising for
potential dense fog over inland and southern zones, where low
level winds are forecast to be lightest. The RAP13 and the HRRR
both suggest dense fog will be fairly widespread by morning
while the SREF favors south GA. We adjust temps and dew points
higher on the evening update and maintained some 20/30 POPs
overnight northern zones and reduced POPS somewhat to the south
of I-16 in GA. Dense fog advisories are possible overnight and
this includes the beaches and barrier islands where sea fog is
expected to develop along the land/sea interface.

$$

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
On Saturday, the forecast area will remain between large high
pressure over the Atlantic as a cold front remains west of the
Appalachians. The south winds should bring upper 50s to low 60s
dewpoints north across the shelf waters, supporting areas of sea fog
and patchy fog across the beaches and coastal areas. South return
flow is forecast to gradually strengthen across the CWA, providing
weak WAA. Forecast soundings indicate a building H85 inversion
through Saturday. I will keep SCHC PoPs across the far inland GA and
SC counties, keeping most of the CWA dry. High temperatures are
forecast to range in the low to mid 70s.

Sunday, the overall pattern changes little from Saturday. However,
deeper moisture should build over the forecast area as the cold
front reaches the southern Appalachians late Sunday. Forecast
soundings indicate that the inversion will lower to H95, with
greater elevated instability. Short range guidance shows showers and
a few storms developing across southern AL/GA during the morning,
lifting NE across the CWA during the afternoon hours. I will
forecast increasing PoPs through Sunday morning and afternoon,
ranging from likely inland to CHC over the near shore waters, with a
SCHC for thunder. High temperatures are expected to warm around
three degrees from Saturday.

Sunday night into Monday, the cold front will slow drift east across
the Southeast, slowed by nearly parallel flow at H7 to H5. Pre
frontal convection will gradually increase as the front approaches
the region, highlighted with categorical PoPs inland to likely
values east. I will include a mention of thunder during the daylight
hours. The CWA will remain on the warm side of the front through the
day, with highs ranging in the low to mid 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Models are in decent agreement on the synoptic pattern through the
long term period. Surface high pressure will wedge down the eastern
seaboard Tuesday as a cold front becomes stationary either offshore
or across our southern zones. Precip chances will remain in the
forecast given proximity to the front. The surface high will
eventually expand over the region midweek and persist through at
least Thursday. Temperatures will continue to be above climo.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
KCHS: steady rains and occasional MVFR cigs this evening with
rains diminishing toward 03Z to 04Z. Low clouds and fog should
begin to develop in the wake of the rains overnight.

KSAV: MVFR/IFR cigs should trend more toward IFR/LIFR overnight
as stratus decks tend to expand and build down.

A warm front will lift north this evening and overnight while
surface moisture significantly ramps up. Only slow improvement
expected late Saturday morning at both with visibility
improving though ceilings will likely remain MVFR for much of
the day.

Extended Aviation Outlook: Flight restrictions likely in fog and/or
stratus each night through early next week. Flight restrictions also
possible in showers/thunderstorms late weekend through Tuesday.

&&

.MARINE...
Winds/seas have remained somewhat elevated along the SC coast as
pinching gradients have been slow to relax. We adjusted some 3
hour wind speed trends with onshore flow in this region. The
flow will gradually diminish overnight as the coastal warm front
lifts north. Seas will remain in the 3-4 ft range near shore
and 5 ft beyond 20 NM but slowly begin to subside late as the
flow decreases.

Reports from the Charleston pilot boat reported low cigs and vsbys
down to 2 NM at times while the Savannah pilot boat reported
near zero vsbys outside the river entrance. We just issued a
Dense Fog Advisory for the near shore GA waters into the
southern SC waters. Sea fog will likely expand north overnight
as 60F dewpoints move over the low/mid 50s nearshore water temps
and low-level winds decrease considerably.

Saturday through Wednesday: The sfc pattern will remain between
Atlantic high pressure and a slow moving cold front to the west.
This pattern will support steady south winds, generally ranging
between 10-15 kts. Wave heights are forecast to range from 2-4 feet
within 20 NM to around 5 feet beyond 20 NM. Marine thunderstorms are
possible on Sunday. The cold front is forecast to move through early
Tuesday although will linger nearby through the day. High pressure
will expand over the region on Wednesday.

Sea Fog: A warm and very humid air mass will overspread the cooler
shelf waters over the weekend. This will lead to a risk of sea fog
Saturday through early next week.

&&

.EQUIPMENT...
The KCLX radar remains out of service until further notice due
to major equipment failure. Repairs are ongoing. Adjacent
radars include: KLTX, KCAE, KJGX and KVAX.

The Downtown Charleston observation site (CHLS1/KCXM) is having
occasional data issues. Use data with caution.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Dense Fog Advisory until 2 PM EST Saturday for AMZ352-354.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
EQUIPMENT...



Area Forecast Discussion

National Weather Service Des Moines IA

 535 PM CST Fri Feb 9 2018

.SHORT TERM.../Tonight through Saturday/
Issued at 304 PM CST Fri Feb 9 2018

Next round of snow expected for mainly southern Iowa tonight.
Forcing ahead of the next shortwave to impact Iowa will increase and
shift across the state from mid to late evening through about 12Z in
the southeast.  The strongest forcing will be in a fairly narrow
band across southern Iowa...likely across the highway 34 corridor
but strong mid-level forcing will exist all the way to the I-80
corridor.  High-res models were initially pegging the highway 34
corridor but through the day were gradually shifting north and
coming more in line with the NAM.  I still believe the NAM is too
far north bringing the higher qpf a little north of the I-80
corridor and given that the qpf for the GFS, RAP and the HRRR was
about a tenth of an inch less overall...some tweaks/blends were made
to the qpf in both amount and location taking the other models into
consideration. Snowfall amounts will be somewhat tricky since this
strong forcing is mainly mid level but the moisture is deeper and
the forcing does tap into it and it is within the better dendritic
growth zone of -10 to -20 degrees C. Putting it all together gives
us an expected snowfall of around 3 inches near the I-80 corridor
with 4 inches or so around the highway 34 corridor.  A winter
weather advisory will be issued for this area to coincide with when
the better forcing moves in.

By the 12-15Z timeframe the forcing is exiting to the east and while
some light snow may continue towards mid morning Saturday, the bulk
of the accumulating snow for our forecast area should be done just
after 12Z.  The remainder of Saturday should be dry ahead of the
next system to impact the state but clouds will remain over the
state and it will cold.

.LONG TERM.../Saturday night through Friday/
Issued at 304 PM CST Fri Feb 9 2018

The next and last in a series of systems to affect the state will
arrive on Saturday night. Surface features will be well south of
the state with almost all forcing residing in the mid levels
associated with the passing shortwave. The increased forcing will
quickly saturate the atmosphere during the evening with snow
spreading northward to around the Highway 92 corridor by midnight.
The snow area will extend a bit farther north across the eastern
CWA reaching the I80 corridor near Grinnell. With the forcing
persisting overnight, anticipate light snow to continue until
shortly after daybreak in the far southeast before subsidence and
drier air arrive. With the snow ending Sunday morning in the
southeast, quiet weather is expected the remainder of the day
across central Iowa albeit rather cold with a canadian airmass in
place along with extensive snow cover.

Much of the upcoming week will see quiet weather as system drops
down the west coast and becomes cutoff. There will be some
moderation by midweek as the upper flow flattens somewhat across
the CONUS, however this reprieve from the colder weather appears
short lived as additional polar will be poised to arrive by the
end of the next work week.

&&

.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 532 PM CST Fri Feb 9 2018

Area of snow and MVFR cigs area expected to impact southern IA
including the KDSM/KOTM areas overnight. Visibilities may drop to
IFR or below at times. The snow will end late tonight into
Saturday morning and conditions will return to VFR. Little to no
impact at other sites with VFR conditions expected to persist.
Northerly winds at less than 12kts will continue through Saturday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to 7 AM CST
Saturday for IAZ057>062-070>075-081>086-092>097.

&&

$$

SHORT TERM...FAB
LONG TERM...Cogil
AVIATION...Donavon



Area Forecast Discussion

National Weather Service Lincoln IL

 922 PM CST Fri Feb 9 2018

.UPDATE...
Issued at 900 PM CST Fri Feb 9 2018

Expired Winter Weather Advisory across far northern portion of
the forecast area a little early as persistent snow band weakened
and shifted off to the east.

A weak disturbance in the broad troffing across the lower 48
states is tracking east-northeast toward the Midwest from the
central Plains. This disturbance has resulted in an area of light
snow across Iowa, and this should impact far northern portion of
forecast area after midnight, although accumulations are not
expected to be significant. Otherwise, persistent/weak isentropic
upglide remains over the entire area, with spotty weak returns
evident on area radars. Away from the main approaching
disturbance, any precipitation is likely to be freezing
drizzle/drizzle or possibly flurries due to a relatively low
supply of ice crystals. Do not expect much icing with any freezing
drizzle that occurs. Some of the high-resolution guidance suggests
light snow will be a little more widespread across central
Illinois, but sounding profiles are not supportive of much snow
away from the approaching disturbance.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 330 PM CST Fri Feb 9 2018

Extended the winter weather advisory through 9 pm for Knox, Stark
and Marshall counties, and added Peoria and Woodford counties to
the advisory. Additional snowfall amounts of 2 to 3 inches
possible through 9 pm in these counties, with storm totals of 3-6
inches along and north of a Galesburg to Lacon line. A special
weather statement will also be issued for areas from I-72 south
for the light freezing rain/glaze possible from overnight into
Sunday morning with the most widespread freezing rain occurring
Sat night into early Sunday morning with one to two tenth inch of
ice possible in southeast IL.

The 21Z/3 pm surface map shows a cold front pressing southeast of
a Danville to Shelbyville line. Mild temps of 50-55F ahead of this
cold front in southeast IL, while much colder temps of 20-25F nw
of the IL river. Colder air ushered into central and nw IL on
northerly winds ahead of 1037 mb arctic high pressure over MT and
ridging over the northern plains. The freezing line extended from
Jacksonville to Lincoln to Gibson City. The cold front will push
through southeast IL through mid evening. An 850 mb frontogenetic
forced band of snow was sinking slowly southward over Knox, Stark
and Marshall counties past few hours and vsbys below 1 miles at
times in heavier snow band. Latest CAM models like the HRRR and
RAP show this snow band lingering over the advisory area until
03Z/9 pm before it weakens and departs to the east. More snow
showers to spread east from the central plains into central IL by
overnight into Sat morning. Could also see patchy light freezing
rain/drizzle south of I-72 overnight into Sat morning as well.
Lows tonight range from 12F at Galesburg to 32F at Lawrenceville.

A bit of a lull in precipitation chances later Saturday morning
and Sat afternoon with pops just ranging from 20-30% then.
Continued patchy freezing light rain/drizzle from I-72 south with
light snow chances north of I-72. Areas south of I-70 to get warm
enough for just light rain chances late Sat morning into early Sat
evening. Highs Sat range from around 20F nw of the IL river, to
the mid 30s Southeast of I-70.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 330 PM CST Fri Feb 9 2018

The cold front will stall out this weekend southeast of the Ohio
river over the TN and eastern Ohio river valley as a couple weak
surface low pressure system track ne along it. This will like
spread mixed precipitation across central and southeast IL Sat
night and Sunday morning and diminish Sunday afternoon. Freezing
rain appears to get as far north as I-72 Sat night and confined to
southeast IL Sunday morning, with light snow chances north of
there. Between one and two tenth inch ice possible in southeast IL
with a light glaze as far north as I-72. Between 1-3 inches of
snow possible north of I-72. Another winter wx advisory may be
needed during that time frame especially for areas south of I-72.
Cold highs Sunday in the lower 20s northern CWA and around 30F in
southeast IL. Skies clear from the nw during Sunday night and nw
winds diminish giving us a very cold night. Lows Sunday night
range from zero to 5 below northern CWA over deeper snow cover,
and mid teens in southeast IL southeast of I-70.

Dry weather finally returns to area from Sunday night through
Wed morning as 1041 mb Canadian high pressure settles se into the
Great Lakes by Monday. Below normal temps continue Monday despite
ample sunshine, with highs ranging from mid 20s northern CWA to
mid 30s in southeast IL. Lows Mon night around 10F northern CWA to
lower 20s in southeast IL. Semi-zonal upper level flow for middle
of next week and developing sw winds on Tue to bring in milder
temps for mid week. Highs Tue range from low to mid 30s northern
CWA to mid 40s in southeast IL. Even milder on Wed with highs
40-45F northern CWA and lower 50s in southeast IL. Have slight
chance of light rain showers in southeast IL Wed afternoon.

Stuck close to consensus of models for forecast during 2nd half
of next week, which has chances of rain showers Wed night through
Fri. Rain chances possibly mixed with snow or turning to all snow
chances over central IL Thu night into Fri morning as cooler air
arrives behind a cold front pushing toward the Ohio river by
sunset Thu. Highs Thu range from lower 40s by Galesburg to mid 50s
by Lawrenceville. Highs Fri range from mid 30s northern CWA to
mid 40s south of I-70.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 558 PM CST Fri Feb 9 2018

Predominantly MVFR condtions expected across the central Illinois
terminals through the 00Z TAF valid time, although local IFR
condtions are possible from time to time tonight. Have generally
not included precipitation mention, due to expected low coverage
and low confidence in exact timing/location. However, some light
snow and/or patchy freezing drizzle is possible. Northerly winds
will persist through the period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Bak
SHORT TERM...07
LONG TERM...07
AVIATION...Bak



...Update to aviation forecast discussion...



 .SHORT TERM...(This evening through Saturday)
Issued at 259 PM CST Fri Feb 9 2018

20Z water vapor imagery shows broad cyclonic flow over North America
with a sheared out shortwave or two over the northern Rockies. This
pattern leaves somewhat zonal flow over the central plains.
Meanwhile a Canadian high pressure system at the surface continues to
move south. The cold front has pushed through and stretches from
northwest OK into western MO.

For tonight the main concern is the potential for some freezing
drizzle to develop this evening. All of the guidance is showing a
warm air advection pattern developing over the surface high with
some isentropic upglide developing over east central KS. However
this lift does not persist for very long as the NAM and RAP progs
show the upglide below 800mb going away shortly after midnight.
Additionally forecast soundings show the better vertical motion
from the isentropic lift occurring within the top or just above the
saturated level while maintaining some dry air near the surface.
Another complicating factor is much of the stratus over east central
KS has scattered out. So the models continue to show some potential
for freezing drizzle but there are also signals working against
drizzle. Have a slight chance for some freezing drizzle over east
central KS with no real accumulations. Considered a winter weather
advisory for travel concerns, but with marginal confidence in
drizzle developing will opt to hold off and let the evening shift
monitor trends. Another thing to watch out for is the chance for
some light snow across the far northern counties. There has been
light snow moving across central NEB much of the day where the mid
level frontogenesis has set up. Models show the frontogenesis moving
south through the night but keep the mid level saturation just north
of the state line. Therefore think any accumulating snowfall is more
likely to remain north of the forecast area. Nevertheless have some
chance POPs overnight for the possibility of snow. Lows tonight
should not drop off to much as models keep good mixing of the
boundary layer with mostly cloudy skies likely to persist. So have
stayed pretty close to the prev forecast of lows from around 8 north
to the middle teens south.

By Saturday morning, the warm air advection pattern is progged to be
gone with cold air advection and isentropic downglide over the entire
forecast area. So any freezing drizzle chances are expected to be to
the south and east of the forecast area. Mainly dry conditions are
likely through the morning. By the late afternoon, shortwave energy
is expected to dig into the central Rockies while mid level
frontogenesis slides south across the state. There is reasonable
agreement among the models that some mid level moisture will be on
the increase as the forcing starts to come together. Therefore snow
chances are forecast to be on the increase from west to east through
the afternoon. Forecast soundings support the idea of all snow as
cold air advection persists through the day. Highs are unlikely to
warm much because of this and think they will range from the middle
teens north to the middle 20s south.

.LONG TERM...(Saturday night through Friday)
Issued at 259 PM CST Fri Feb 9 2018

On Saturday evening an upper-level trough axis will extend from
south central Canada towards the central Rockies. The cyclonic upper-
level jet will be positioned over the Great Lakes region and provide
divergence within the right entrance region over eastern KS. That
trough axis progresses eastward Saturday night and Sunday morning.
Ahead of the trough marginal positive vorticity and potential
vorticity advection should add to the large scale lift over
northeast KS. As a result an area of snow should spread across
northern KS during the evening and gradually shift southward
across the entire forecast area by Sunday morning. It appears the
lift resides relatively longer over northern KS resulting in the
higher QPF values. A east to west orientated mid-level
frontogenetical band centered around 700 mb could also transverse
across the area, which may provide additional lift to possibly
enhance snowfall rates. As of now the models are in fairly good
agreement with a nearly saturated profile prior to the lift
arriving. An examination of cross sections reveal that the
frontogenesis is initially relatively shallow in depth, flat, and
partially decoupled until the trough axis approaches from the west
Sunday morning. There are also hints of decrease EPV above these
levels that could contribute to some banding within the larger
area of snow. The dendritic growth zone is the deepest over
northern KS late Saturday evening, but not much over 100 mb which
is supported by SREF probabilities and model soundings. This along
with cooler temperatures within the column should support snow to
liquid ratios around 15:1 with closer to 12:1 in east central KS
where the DGZ is shallower and the profile is slightly warmer.
Given QPF generally around 0.05 to 0.20" the total snow amounts
range from 1 to 3" with the higher totals north of I-70. Snow
should come to an end as the trough axis swings overhead late
Sunday morning.

Another decent shortwave trough tracks southward over the northern
Rockies early next week, which keeps the area in zonal flow aloft.
This will allow temperatures to gradually warm with highs in the 50s
by Wednesday. The models disagree with how that shortwave evolves
over the southwestern US and when it ejects out over the plains
sometime late next week. This is fairly typical with cut off low
pressures in this region. There is agreement though that the
system weakens into more of an open wave as it lifts northeastward.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 531 PM CST Fri Feb 9 2018

For the 00z TAFs, MVFR cigs were beginning to stream over the TAF
sites, with short-range model guidance showing these cigs
persisting through much of the overnight hours into Saturday
morning. There is some model uncertainty with regards to when
these MVFR cigs will begin to scatter out, so times may need to be
adjusted in future TAF amendments. Winds will remain out of the
north, with the potential for snow beginning to increase by the
end of the TAF period (primarily near KMHK).

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...Sanders
AVIATION...Hennecke