Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/22/17

Area Forecast Discussion

National Weather Service Cleveland OH

 913 PM EST Sat Jan 21 2017

.SYNOPSIS...
Temperatures will remain mild through Monday as low pressure
tracks from the Mississippi valley northeast towards the Mid
Atlantic states. A ridge of high pressure will build across the
region Tuesday into Wednesday. A low pressure system will track
east across the southern Great Lakes Wednesday with more
seasonable temperatures arriving late week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Bumped up pops across NE OH slightly. Expect rainfall amounts to
be on the light side...just a trace to a couple of hundredths of
an inch or rain. With the warm front lingering near the Erie
lakeshore removed mention of fog everywhere except NW OH.

Original discussion...
Precipitation and fog potential overnight are the main concerns in
the forecast. A couple weak mid level impulses will advect northeast
across the area through tomorrow morning. Elevated radar returns
showing up in central Ohio associated with this first impulse have
not been reaching the ground, as soundings show relatively dry
boundary layer. Low level jet centered west of the area this
afternoon will help to moisten the 925-700mb layer. Best shot of
precip will be around and after 06Z as second impulse works toward
the region. For now, kept slight chance of rain showers in the
forecast. Some elevated instability/decent lapse rates could yield a
few isolated thunderstorms, however confidence in precip with weaker
forcing precludes any thunder mention.

Areas of fog are likely to develop after 06-09Z as boundary layer
decouples and winds become light, with a rather strong inversion
forming. Could see some areas of dense fog in the Toledo area and
vicinity, but for now, will hold off on any headlines for dense fog
and just mention areas of fog/patchy dense fog and will monitor this
evening.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY NIGHT/...
Focus of the short term period is precipitation chances Sunday
through early Tuesday. Upper low will slowly track and deepen from
the lower Mississippi valley Sunday morning to the upper Ohio valley
by Monday afternoon in response to strong southern stream jet
energy. Models are in decent agreement with track/evolution of upper
low and attendant surface reflection. The precip arrival Sunday has
trended a bit slower, with much of the morning/earlier afternoon
possibly dry across the forecast area. Adjusted the forecast to
reflect this trend, with chance pops arriving after 17Z and likely
pops holding off until 21Z and after.

Best window for precipitation, and possible heavy rainfall, will be
Monday morning/early afternoon, especially across the eastern half
of the area where cat pops have been expanded a bit. This is where
best forcing will be present as the upper low tracks along the
Appalachians just east/southeast of the area. Kept QPF amounts Sunday
through Monday night ranging from 0.30" west to around an inch east.
Precip will wind down Monday night/Tuesday morning as the low tracks
eastward off the Atlantic coast. One wild card in the Monday night
time frame is p-type. ECMWF and GFS tend to be on the warmer side
with the low, with perhaps a brief period of changeover to rain/snow
mix late Monday night. The NAM, however, wraps much more colder air
into the low, with p-type changing over much earlier Monday evening,
and perhaps a changeover to all snow overnight, with some
accumulation possible. For now, discounted the NAM and went with a
GFS/ECMWF blend for column temperatures and resultant p-types, with
rain and snow mentioned Monday night. This solution will need to be
watched over the coming model runs and the forecast will be adjusted
accordingly.

High pressure ridge will build across the region Tuesday. This
should yield dry conditions much of Tuesday and Tuesday night.
Northern stream wave will track from the central Rockies toward the
Great Lakes, with precip arriving towards 12Z across the area. P-
types may be in issue, especially NE OH/NW PA high elevations, but
it is too early for specifics other than a cursory rain and snow
mention.

Temperature wise, went a few degrees warmer for highs on Sunday with
slower precip arrival trend, near MAV/EC MOS, but not as warm as MET
MOS. This yields upper 50s/mid 60s across much of the area.
Temperatures will trend cooler Monday through Tuesday, but still
well above seasonal normals.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The long term begins on Wednesday with models in good general
agreement showing an upper over the upper midwest and a general
southwest flow aloft over the area. At the surface, low pressure
will be in SERN MN with a warm front into western Ohio and a cold
front south from the low through Indiana. The low will move
northeast across the Great Lakes dragging both fronts across the
region during the day. Temps will fall behind the cold front
changing rain Wednesday into snow Wednesday night. Thursday 850mb
temps should be around -5C which should keep most precip snow during
the day. Continued with chance pops most places although did keep
likely northeast with flow off the lake for potential lake
enhancement although it would be minimal given temps. No big change
Friday although 850mb temps continue to slowly drop.  Friday night
into saturday another trough rotates across the region bringing
colder air to the region with 850mb temps dropping to -10c and
likely continuing lake effect enhancement northeast.

&&

.AVIATION /00Z Sunday THROUGH Thursday/...
VFR weather continues all areas with mainly mid and high level
cigs. Some showers remain just south and southeast of the area.
The latest guidance including the HRRR has this activity
dissipating by 06z. Will go with a vicinity mention at CAK and YNG
for a few hours. If the precip becomes more imminent we will
update. A strong inversion will develop overnight as cooling
occurs at the surface. This should cause fog and stratus to
develop. Conditions will be the worst in the west...possibly LIFR.
Will develop MVFR cigs all areas around 08z with patchy IFR fog
after that. Will try to improve cigs back to VFR on Sunday morning
with precip holding off till the tail end of the TAF period.

OUTLOOK...Non-VFR developing Saturday night continuing into Monday
in rain. Non-VFR will likely persist on Tuesday across NE OH/NW PA.

&&

.MARINE...
Light south to southeast flow on the lake today through tonight as a
warm front lifts north of the lake. Flow will remain light Sunday as
it turns out of the northeast in response to low pressure moving
through the Tennessee valley. This northeast flow will increase
Sunday night reaching 15 to 20 knots overnight and 20 to 25 knots on
Monday before turning north and dropping back to 10 to 15 knots
overnight Monday night. Winds will increase again from the southwest
Wednesday to 15 to 25 knots as low pressure moves through the
central lakes. Would anticipate small craft headlines will be needed
early Monday into/through Monday night and late Wednesday into
Thursday.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.

&&

$$
SYNOPSIS...Greenawalt
NEAR TERM...DJB/Greenawalt
SHORT TERM...Greenawalt
LONG TERM...TK
AVIATION...Kubina
MARINE...TK




Area Forecast Discussion

National Weather Service Grand Forks ND

 936 PM CST Sat Jan 21 2017

.UPDATE...
Issued at 931 PM CST Sat Jan 21 2017

Latest METARs are showing some lower vsbys in fog from Grand Forks
Air Force Base up through Cavalier...with obs mostly around 1/2SM.
will need to monitor this area as HRRR does indicate this thorugh
the overnight period. East of the river, light echoes over NW
Minnesota are likely producing some patchy drizzle in areas but
with temps just above freezing not expecting any impacts. Patchy
drizzle is covered in forecast but did change wording from
probability to coverage. Also FAR has recently dropped to
1/4SM...increasing concern this will spread up the valley. No
changes to headlines yet but will expand if necessary.

UPDATE Issued at 602 PM CST Sat Jan 21 2017

Forecast update addresses fog issues beginning to develop across
portions of southeastern North Dakota into the southern Red River
valley. Web cams showing fog development from Tenney, MN through
the Oriska rest stop east of Valley City...to include Gwinner that
is now showing 1/4SM visibility. Will issue a dense fog advisory
for the I-94 corridor and south...to include Cass/Clay counties as
well as western Otter Tail. Confidence not as high for the Fargo
Moorhead area but certainly expect visibilities less than one
quarter mile to develop in far western Cass and far southern Clay
over the next couple of hours...especially since Moorhead ob
currently showing zero dewpoint depression and calm winds. Dense
fog advisory will be in effect through noon Sunday.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 253 PM CST Sat Jan 21 2017

Same challenges continue for tonight with fog, drizzle and
potential for freezing pcpn later this evening possibly impacting
travel.

Broad upper trough remains over the n central US. From water
vapor imagery appears to be a weak mid level shear axis in central
ND shifting east. A weak surface trough bisecting ND from NW-SE
also expected to drift east tonight. Ahead of these features there
are some lower condensation pressure deficits and there is some
weak isentropic lift from the valley west which weakens overnight.
With some spotty radar returns over the far western fa will keep
some chance pops for measurable pcpn. Only catch is soundings
more supportive of drizzle vs r/zr/s. For this will limit any
measurable pcpn potential to the west and later shifts will have
to adjust if necessary. Overall not much drop in temperatures
overnight as in the past few nights although may be a little
cooler in the nw. Visibility over the west has improved so degree
of fog and if dense in question but with all the low level
moisture feel there will be some degree of fog and will keep the
mention in the forecast.

As weak trough passes tomorrow does not appear to be a great deal
of lift so for the most feel the day will be dry. Maintained some
low end pops but confidence low and if anything and continuance of
some dz/fzdz. Temperatures will continue to be above average but
maybe a tad cooler with some cooler air moving in.

.LONG TERM...(Sunday night through Saturday)
Issued at 253 PM CST Sat Jan 21 2017

The advent of more westerly upper level flow Sun night should start
to scour out most of the stratus/dz/fzdz with areas of -sn becoming
more prevalent as column cools with time. Most if not all of this
pcpn will be east of the valley Sun night. Mon will be dry but will
still offer a fair amount of cloud cover in the absence of any
strong high pressure. Guidance differs a bit on the track of the
next system for Tue but it appears that movement through Iowa or
extreme southern MN will still brush the far southern forecast
area with minor snowfall amounts.

Wed through Sat...

12z GFS/ECMWF continue to indicate low pressure and associated
system moving toward lake Michigan as this period begins on Wed. It
still appears that the northern edge of the pcpn shield should clip
parts of SE ND and the southern tip of our MN lakes region as it
pulls out. This is handled well in the fcst with minimal
accumulations over this part of the forecast area. Cyclonic flow and
some upper level trough could lead to brief periods of light snow
region wide during Wed into Thu. Temps will be generally dropping
through the week albeit still above average with highs in the 20s
instead of the 30s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 602 PM CST Sat Jan 21 2017

Expect primarily IFR cigs with lowering visibilities in the
southern RRV this evening. May see some brief periods where cigs
increase into MVFR range but this should be short lived.


&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Dense Fog Advisory until noon CST Sunday for NDZ038-039-049-052-
     053.

MN...Dense Fog Advisory until noon CST Sunday for MNZ003-029-030-040.

&&

$$

UPDATE...Speicher
SHORT TERM...Voelker
LONG TERM...WJB
AVIATION...Speicher




Area Forecast Discussion

National Weather Service Hastings NE

 1001 PM CST Sat Jan 21 2017

.UPDATE...
Issued at 1001 PM CST Sat Jan 21 2017

Witnessed some patchy fog in Hastings and a few sites have also
reported brief periods of reduced visibilities. Confirmation of
the patchy fog on webcams was not fruitful, but the low patchy fog
witnessed at the office supported the obs. Currently believe the
fog will be patchy in nature and only reduce visibilities to a mile
at times. Expanded the mention of patchy fog in the forecast
westward through morning. The latest RAP give some support for
brief periods of fog/reduced visibilities moving across the
eastern portions of the area. Currently am not expecting
widespread dense fog.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 157 PM CST Sat Jan 21 2017

Aloft: A very complex trof was over the Cntrl/Wrn USA with
multiple embedded shortwave trofs. A shortwave ridge was over the
Cntrl Plns between the small low that moved thru yesterday...and
the next one in the process of forming over TX. This low will
remain well S of the region thru tonight...leaving the fcst area
in quiet wx.

Surface: It`s highly unusual...but broad low pres was over the
Plns. There really was no high pres in the wake of yesterday`s
system... just a hint of a ridge across MO/KS/NE. Cyclogenesis was
underway over the TX Panhandle. This low will head E across OK and
into AR tonight...remaining safely to the S.

Tonight: Increasing clouds. Becoming p-m/cloudy. Another night of
low temps about 15F above normal.

Sun: p-m/cloudy in the morning...then clearing in the afternoon.
Another mild day...similar to today but a little cooler over
S-cntrl Neb.

NW winds will gust 18-24 kts.

.LONG TERM...(Sunday night through Saturday)
Issued at 157 PM CST Sat Jan 21 2017

Aloft: NW flow will gradually strengthen Sun into Sun night as a
shortwave ridge approaches ahead of a new trof moving onshore in
the W. The ridge will move thru Mon. The Wrn trof will be complex
with multiple embedded vort maxima...one of which will induce
cyclogenesis Tue and the formation of a new low. This low will
head E across Neb/KS Tue. A broad trof will be left in its wake
Wed-Fri. Fri its axis will pass thru the fcst area followed by N
flow as a Wrn ridge/Ern trof evolves.

Surface: Weak/small high pres will build in Sun and then cross
the fcst area Sun night. Lee cyclogenesis will commence over CO
Mon along with warm frontogenesis down into the Srn Plns. There
are still substantial timing and intensity diff`s in the last 2-3
runs of the NAM/EC/GFS/CMC and the 09Z SREF mean...but the basic
idea is that this low will eject ENE across KS Tue. Colder air
will be drawn S into the region Wed as this low heads into the
GtLakes...and high pres expands from N-S thru the Plns. Another
cold front will probably move thru Thu followed by high pres Fri-
Sat.

Some Sensible Wx Details...

Mon: Quiet. Another nice day. Probably averaged p/cloudy most
locations. Temps still 10-15F above normal.

Tue-Wed: Kept the fcst pretty generic. There is significant
uncertainty on where/when/how much pcpn will fall and what type(s)
of pcpn will fall.

Models: The 00Z/06Z/12Z GFS are faster and weaker. The 06Z/12Z
NAM were Srn outliers...ejecting the low into the OK Panhandle.
The 00Z/12Z EC/CMC were deeper and slower...with the CMC the
slowest outliers. 460 mi separate the fastest GFS run and slowest
CMC run at 06Z/Wed. Interestingly...the 12Z run of each model was
consistent with its prvs runs...maintained separate camps.

QPF: Models are all over the board...ranging from little or
nothing...to a light or moderate winter storm for parts of the
fcst area. This system is not occurring in a completely cold
environment. Some areas will probably see some rain.

This system will struggle to produce pcpn...especially in the
warm sector. It will be moisture-starved and most if not all of
the pcpn will be collocated with the strongest lift N of the low.

Bottom line is don`t take our fcst literally yet. The models need
to line up better and converge on a solution.

There are a couple things that we do have higher confidence on:

1) It will be windy with this storm...probably windier than we
currently have in the fcst...especially if the deeper EC/CMC
verify.

2) Turning colder Wed-Sat behind this low...but not excessively
so. Temps return near or slightly below normal.

Can`t rule out some flurries or a brief snow shwr or two...
especially as the upr trof comes thru Fri.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday evening)
Issued at 530 PM CST Sat Jan 21 2017

VFR conditions are expected to prevail. Light and variable winds
will become north to northwesterly overnight. Northwesterly winds
will increase during the day Sunday. High clouds will stream in
overnight, but are expected to clear during the morning Sunday.


&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&

$$

UPDATE...Billings Wright
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Billings Wright




Area Forecast Discussion...Updated

National Weather Service Saint Louis MO

 901 PM CST Sat Jan 21 2017

.UPDATE...
Issued at 857 PM CST Sat Jan 21 2017

Have attempted to update PoPs thru Sun based on latest guidance.
In the near term, seems the HRRR has a decent handle on precip
overnight. Attempted to hold onto precip across wrn and into nwrn
counties into Sun morning and delaying a band of precip moving nwd
into srn counties. However, given the amount of uncertainty, did
not want to make drastic changes to forecast for tomorrow until
more data is analyzed.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 330 PM CST Sat Jan 21 2017

Low pressure centered over northeast New Mexico will begin moving
eastward tonight as the shortwave aloft ejects into the Great
Plains.  Short range guidance has slowed the timing of the onset of
precip into the late evening and overnight hours for most locations;
this is especially true for the convection allowing models such as
the HRRRs and WRFs.  This looks reasonable given the weak forcing
over the area for most of the evening.  That changes as the
shortwave shifts into eastern Oklahoma after 06Z, pushing the low
level circulation with it. RAP/GFS/NAM all show strong low level
moisture convergence wrapping around the circulation up over the
Ozarks by 06Z.  The moisture convergence weakens somewhat after 09-
12Z as the low level flow swings around to the east and then
northeast with the low moving through northern Arkansas.  Expect
widespread showers...and a few thunderstorms more or less along and
south of the I-70 corridor with this system, but think precip
further north will be more spotty since most of the moisture
convergence will be focused south of I-70.  Should see rain ending
slowly from northwest to southeast Sunday with most of the area dry
before 00Z.  Thunderstorm potential tonight should be limited to
areas along and south of I-44.  Forecast MUCAPE values drop off
quickly from around 1000 J/Kg this afternoon to 300-500 J/Kg this
evening.  Can`t rule out a few rumbles of thunder with values like
that, but don`t think there`s enough instability for more than
"isolated" thunderstorms.  Very mild temperatures for mid-late
January will continue tonight and Sunday...although with rain and
cloud cover it`ll be cooler than today.  Guidance lows ranging from
the mid 30s in northeast Missouri to near 50 in southeast Missouri,
and highs of 45 to near 60 look reasonable.

Carney

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 330 PM CST Sat Jan 21 2017

The strong storm system center that will have passed to our south
will be pulling away on Sunday evening and some leftover rain can be
expected, mainly for areas to the south and east of STL metro.

After a brief interlude of a weak RIDGE thru our region late Monday
into early Tuesday, another strong Pacific storm system will
approach late Tuesday.  The models continue to show that the bulk of
the lift with this system will pass to our north on Tuesday night,
but have trended just a tad more southerly with the track over the
past 24hrs.  PoPs across our northern CWA have been edged higher as
a result.  Unlike with the last system on Sunday, enough cold air
will try to seep in during the late night and early morning hours to
justify some mention of snow for pcpn-types as well as rain.

A strong lobe of sheared vorticity aloft will couple with a surface
cold front as they drop thru on Tuesday night and carryover into
Wednesday.  Some limited PoP chances continue, but mainly north of
Interstate 70 with a mostly rain but some possibility of snow mixing
in during the cooler times of day.

Heading into Thursday and into next weekend, models continue to show
additional weak upper level disturbances sliding down into our
region from the resultant northwest flow aloft as a longwave TROF
carves into the eastern CONUS.  However, the column gets
progressively drier decreasing any confidence on the ability of any
one event to successfully precipitate given the lack of strength
currently depicted with any of them.  Have favored a dry forecast
for now until this changes.

Otherwise, temperatures are expected to remain above average until
the middle of next week when the longwave TROF develops, with
temperatures more appropriate for late January heading into next
weekend.

TES

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 539 PM CST Sat Jan 21 2017

Low system continues to develop over the Plains and will swing
into the region on Sun. Elevated TSRA have developed across AR
heading into srn MO. Much of the guidance has slowed onset of
precip at terminals and raised doubt that precip will reach KCOU,
esp KUIN.

A lot of question on cigs and visbys tonight. There is a fair amnt
of guidance that wud suggest much of tonight remains VFR, but is
also some guidance that suggests IFR. Trended visbys and cigs more
twd the VFR/MVFR, but did not see too much evidence to suggest
drastic changes from the pref TAFs. Will continue to monitor.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX




Area Forecast Discussion

National Weather Service Memphis TN

 605 PM CST Sat Jan 21 2017

.UPDATE...

Updated for the 00z Aviation Discussion.

&&

.PREV DISCUSSION... /issued 559 PM CST Sat Jan 21 2017/

UPDATE...
Updated for lowering evening POPs across the northern Midsouth
counties.

DISCUSSION...

Timing of convective development now in the ARLATEX suggests
activity will mainly affect Midsouth points south of a Jonesboro
Arkansas to a Corinth Mississippi line before midnight...with
points to the north getting in the main action afterwards. Made
adjustments to the evening POPs accordingly.

Greatest severe threat will still be large hail...with the most
favorable region for an isolated tornado to the south of I-40 and
west of I-55.

JAB

&&

.PREV DISCUSSION... /issued 333 PM CST Sat Jan 21 2017/

Currently... at 3 PM CST around the Mid-South, clouds are
overspreading the region now with latest H5 analysis depicting
southwest flow present aloft as a mid-level trough axis ejects out
of the desert southwest and into Texas. This trough and upper low
will bring the region a chance for severe weather late this
evening and tonight.

Clouds will continue to build into the region late this afternoon
and evening. Models continue to work out around 1000 J/KG of
SBCAPE for portions of the southern half of the FA, primarily
over the Mississippi Delta region. A warm front will slowly lift
north into the region as a surface low develops to the west in
association with the upper low. This will allow lifting of some
surface based instability, overcoming any atmospheric capping and
producing the chance for strong to severe storms. The latest SPC
outlook has a moderate risk just to the SW of the region, with an
enhanced risk reaching into SW counties of the local FA. This area
will have the best chance for strong to severe storms this
evening as the warm front moves through the region, most likely
between 8 and 10 PM for the SW counties of the FA. While large
hail will be the primary threat given steep mid-level lapse rates
as heights fall rapidly aloft with the approaching trough, enough
shear could be present along the surface boundary for an isolated
tornado or two. In addition, damaging winds could also be possible
from strong downdrafts. While the greatest threat of severe
storms will be over the Mississippi Delta region, after 10 PM
there will be a slight risk for severe storms moving into the rest
of north Mississippi, eastern Arkansas, and west Tennessee. The
latest HRRR composite reflectivity guidance suggests any discrete
storms developing to our SW conglomerating into a more linear form
of storms before affecting the Mid-South.

Showers and thunderstorms will continue overnight and into Sunday
as the upper low moves toward and over the region, although the
severe threat will come to an end by the early morning hours of
Sunday. Sunday highs will be quite cooler than Saturday`s as winds
become more northwesterly as the low passes over the region. By
early Monday both the surface and upper low will be east of the
region, with conditions drying as highs only reach the lower 50s.
Dry conditions will maintain for Tuesday, with an upper ridge
moving overhead allowing temperatures to warm again into the 60s.
By early Wednesday a cold front associated with a surface low to
the north of the area will swing across the region. Models have
continued to trend drier with this feature, thus have only
included slight pops in eastern portions of the FA. Mild
temperatures midweek will become more seasonable for late in the
week as conditions dry once again.

ZDM

&&

.AVIATION...00z TAFs

VFR conditions will continue through the evening hours before
deteorating around midnight. MVFR or lower cigs and vsbys will be
possible early Sunday morning at all terminals as thunderstorms
move across the region. Winds will remain southeast between 5-10
kts overnight. A few severe storms will be possible overnight with
hail the greatest threat.

Widespread showers and thunderstorms will continue across all the
terminals through Sunday as a slow moving upper level low moves
across the region and helps destabilize the atmosphere. Winds will
increase from the southwest by Sunday afternoon at all sites.

JLH

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$




Area Forecast Discussion

National Weather Service Blacksburg VA

 920 PM EST Sat Jan 21 2017

.SYNOPSIS...
A weak warm front south of the area will continue to be the
focus for impulses to travel along overnight into Sunday,
resulting in added rounds of rainfall tonight through Sunday
afternoon. The front should lift north into the region Sunday
night as a stronger area of low pressure approaches from the
west. This low pressure system will slide slowly east across
across the area Monday before exiting Monday night, allowing
for drier weather under high pressure for Tuesday.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 830 PM EST Saturday...

One wave of mostly light rainfall moving through the CWA this
evening producing mostly 1/4 to 1/3 inch rainfall amounts. All
of the synoptic scale and short-range models show that this
first wave and associated negatively tilted upper short wave
will move out of the area this evening. The next wave arrives
Sunday late morning, the activity now being manifested as severe
thunderstorms along the central Gulf Coast. This activity will
not be severe when it reaches the RNK CWA. Rainfall with that
wave appears comparable to the current one. In between,
increasingly deep southwest diffluent flow aloft could result in
light rain at almost any time, but nothing indicated by any
model that generates much concern in terms of heavy rain. More
substantial rainfall arrives Sunday evening along with the
threat for some convective elements, although latest model
severe weather parameters for our CWA look limited. The most
significant period of rainfall and potential for storms should
affect the CWA in the 21Z Sun - 06Z Monday time frame.

Am concerned about fog development again tonight. Currently, the
rainfall is suppressing fog development. However, with weak
wedge in place and wet ground along with light winds, seems like
fog development would be fairly probable again as the night
progresses. Will continue to monitor and issue SPS or DFA/NPW if
needed.

As of 305 PM EST Saturday...

Active near-term forecast period begins tonight continuing into a
good part of the short-term period due to multiple rounds of steady
rainfall to affect the Blacksburg forecast area.

Late-afternoon surface analysis depicts a 1003 mb low near Atlanta,
enhanced to some extent by ongoing strong convective line marching
across southern Georgia, with eastward-trailing warm front from the
low center to a position from Greenville/Spartanburg SC to just
north of Florence SC to Wilmington NC. Lingering in-situ wedge lies
north of it across our area, keeping most of our forecast area in
the cool, cloudy side. Aloft, diffluent mid-level regime with
increasing 500 mb height falls approaching far southwest Virginia.
Composite radar mosaic reveals band of steady rain along the
northern periphery of warm front/mesolow advancing to the northeast,
its northern extent from Knoxville TN to near Charlotte NC.

For Tonight: First band of steady light to at times moderate rain to
progress primarily across the Grayson Highlands, southside Virginia
and northwestern North Carolina between roughly 21z and 04z per high-
res HRRR and RAP. Highest PoPs are focused across that general area,
with a lower/gradient in PoPs north to northwest essentially west of
the Blue Ridge. Appears that the northern fringe of negative
Showalter indices snakes its way into those aforementioned southern
areas. Included slight chance Thunder mention accordingly, but I did
not want to hit that harder given the best potential for convection
remains well south of our forecast area into central/western NC on
southward. Rainfall amounts for tonight range from a few hundreths
in the northwestern part of the CWA to around four-tenths along the
North Carolina Piedmont into southside Virginia.

In the wake of the rain, indication from most guidance is that the
wedge/CAD rebuilds back in with light east flow. Thus for the after
midnight period, I`ve again introduced patchy fog for most of our
forecast area as we`ll be waiting for the second, more
significant/widespread round of rain approaching from the southwest.
Forecast lows in the mid 40s to low 50s under persistent overcast
and areas of rain showers.

For Sunday: Upper trough closes off in the lower Mississippi Valley
early Sunday morning. Aforementioned warm front then lifts north
across much of our forecast area. This focuses a period of moderate
rainfall with rainfall rates enhanced somewhat by (1) convection -
elevated negative Showalter Indices advect into our central portion
of our CWA per NAM/GFS and (2) potential for southeasterly upslope
enhancement in the foothills and Piedmont areas in Virginia and
North Carolina. SPC maintains a Marginal/5% severe and Slight/15%
severe Sunday, primarily across our Piedmont NC counties into the
southside of Virginia due to strong vertical wind profiles. However
only very marginal if any surface-based CAPE with much of the
already modest instability being elevated. Potential is there for
thunder but given the limited amount of instability owing to early-
day CAD, not thinking we`ll see any severe. A conditionally greater
risk for stronger cells remains well to the south from central NC to
FL and as reflected in SPC`s Day-2 Convective Outlook.

Rainfall stands to be the heaviest during the morning into early
afternoon hours. Interesting that to some varying extent amongst the
12z models there is something of a lull in the rain during the
afternoon. So while PoPs start high-Likely to Categorical, I`ve
tried to show a reduction in PoPs to reflect a break in rain, though
they are still high-Chance (40-50%) and only stand to increase again
from SW - > NE Sunday night. All in all, anticipate a wet Sunday
with at least some rise on area rivers and streams. See the Hydro
section which speaks more to the hydrologic aspect given a few days
of at least steady rains (spanning into the short-term period).

Looking for highs Sunday to range from the mid 50s to around 60.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 245 PM EST Saturday...

Next round of heavier rainfall including possible embedded stronger
storms across the far south will be ongoing Sunday evening as very
strong lift/diffluence arcs north ahead of deep low pressure over
the western Carolinas. This will likely bring the heaviest period of
rainfall given more convective nature under 1.25 inch PWATS
just ahead of the advancing warm front and subsequent possible
triple point just off to the southwest. However just how much of
the south and/or east can work into the warm sector remains in
question, with models showing the low level wedge in the wake of
earlier rainfall holding near the VA/NC border before weakening
by early Monday. Since shear is quite impressive and strength
of warm advection stronger than usual, per such a stacked system
given the upper low passing near the Blue Ridge, opting to
include more thunder mention espcly southeast into Sunday night.
Also cant rule out at least some elevated rumbles elsewhere
overnight espcly Sunday evening southern Blue Ridge where seeing
a brief but strong upslope component. Otherwise pops returning
to categorical into early Monday across the region with lows in
the 40s but perhaps rising some early on.

Upper dry slot may act to cut off showers across the east Monday
morning as the center of the upper low drifts into western VA
and eventually to the east/northeast of the area by Monday
night. This likely to shift bands of heavier rainfall over the
west during Monday as the deformation zone develops aided by
wrap around moisture behind the exiting upper low. However
uncertainty remains espcly by Monday with the track of this
system including the degree of more concentrated heavy rain,
and where precip may be more convective resulting in higher
rates. Models have again shifted east with QPF totals given more
convective nature over the southeast and more in the way of
stratiform rain closer to the low at this point. This on top of
previous rainfall would likely bring the highest threat for
flooding pending exactly where added bands set up, so keeping
mention in the HWO and hydro section of the AFD for now. Highs
Monday remain tricky with potential for values to zoom to around
60 Piedmont while staying in the 40s northwest, with low/mid
50s in between.

Axis of deeper moisture should continue to fan out to the west
before shrinking along the higher western mountains Monday night as
the low and associated lift depart. However increasing upslope
northwest flow in the wake of this system likely to keep showers
going western third overnight, while some drying and cutoff in pops
takes shape east of the Blue Ridge. Temps aloft also appear too warm
for much snow so leaving out mention except highest elevations late
Monday night. Main concern overnight will again be with strong winds
as the low heads offshore and the pressure gradient between high
pressure to the south increases. Latest input of strong subsidence,
brief cold advection and a lowering inversion into local scheme data
off the GFS, still suggests potential wind advisory criteria
mainly NC mountains. Therefore have again included a mention
in the HWO there overnight. Otherwise running with diminishing
pops overnight with only chance pops lingering north/west late
and little elsewhere. Lows mostly 30s to lower 40s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 215 PM EST Saturday...

Strong upper trough will be lifting out on Tuesday making way for a
brief period of shortwave ridging that will slide east and across
the area later Tuesday into Wednesday night. May still be some
upslope driven rain and high elevation snow showers Tuesday morning
before much drier air slides in from the southwest under a nose of
surface high pressure that will extend north from the Gulf coast.
This should bring clearing skies Tuesday afternoon with sunny skies
on Wednesday before clouds increase again later Wednesday night
ahead of the next upstream cold front. Winds should remain quite
strong into midday Tuesday with potential advisory level speeds
espcly NC mountains into far southwest VA. Will be the mildest
period for quite some time with highs 40s mountains to upper 50s
east Tuesday, followed by 50s to lower 60s Wednesday under warmth
aloft and westerly flow.

Return to more winterlike conditions will ensue by weeks end with a
cold frontal passage by Thursday ahead of a broad longwave trough
that will drop south into the region and persist into next weekend.
However latest guidance not nearly as strong or deep with this
feature making for more Canadian type air vs. much colder thickness
seen yesterday that was supportive of Arctic air. However will see
persistent cold advection develop by Thursday with weak passing
shortwaves gradually helping to bring in colder air aloft by
Saturday. A band of showers possible along/behind the front Thursday
into Thursday night although iffy given only sheared southern
energy. Therefore will only include a low pop shower mention
including possible western snow showers overnight. Otherwise will
evolve to mostly upslope driven clouds and periodic light snow
showers far west, to mainly clear/sunny east Friday into Saturday,
under a rather dry and more westerly flow driven environment. Highs
mostly 30s to around 40 mountains to mid 40s east into the weekend.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
As of 658 PM EST Saturday...

Poor flying conditions expected during the taf period with
widespread IFR/LIFR in low clouds,fog and rain.

This evening into tonight, flight categories will lower with
patches of rain and drizzle. Pocket of fog in the east will
degrade ceilings and visibilities to IFR and LIFR conditions
at KROA,KLYH and KDAN. While in the west at KBCB, KLWB and KBLF
expect VFR conditions to lower to MVFR in rain and fog.

Rain will pull out of the east early tonight. Then, in-situ
wedge develops in behind the rain again focusing a period of
IFR to VLIFR conditions due to stratus and fog.

Second wave of steadier rainfall then looks to build from the
southwest during the morning hours Sunday, with coverage of rain
covering a larger portion of our forecast airspace along with
a few rumbles of thunder. Due to low forecast confidence in
specific airports being affected by thunder, did not mention in
the TAF at this point, but the best shot would be at KLYH, KDAN
and KROA. Flight categories IFR to VLIFR through 00z Monday,
due to low ceilings, with visibilities 3-6 SM in rain briefly
heavy at times.

Winds generally light and variable (trending southeast) through
most of the TAF period.

Low confidence in ceilings,visibilities and wind during the taf
period.


Extended Aviation Discussion...

A slow-evolving but potent storm system affecting a good part
of the central and southeast CONUS will lead to a potentially
long period of sub-VFR conditions through Monday with stratus,
fog, and periods of rain, in addition to thunderstorms. Once the
storm passes on Tuesday, conditions will improve with respect to
cigs and vsbys, but it will become breezy with northwest winds
gusting to 30 kts behind the departing storm on Tuesday. High
pressure prevail for Tuesday night and Wednesday night. A band
of MVFR showers possible along/behind the front Thursday into
Thursday night.

&&

.HYDROLOGY...
As of 310 PM EST Saturday...

There will be several rounds of rainfall affecting the Blacksburg
hydrologic service area beginning tonight and lasting through
Monday. The greatest amount of rain over a 24-hour period looks to
be on Sunday with 1 to 2 inches of rain across most of the forecast
area, with lighter rainfall amounts expected tonight across the
southern tier of counties/Dan and Yadkin River basins and again
Monday along and west of the Appalachian Divide into southeast West
Virginia, the Mountain Empire of Virginia and into parts of the New
River Valley.

Using a model blend, heavily weighting WPC in that blend, forecast
rainfall amounts tonight through Sunday range from 1.5" for most of
southeast West Virginia and the Alleghany Highlands, to well over 2
inches along the east-facing slope of the Blue Ridge.

Current expectation is for gradual main-stem river rises with
faster/greater response on smaller rivers/creeks, along with some
potential for ponding on roads and in areas of poor drainage.
Rainfall rates do not appear excessive at this point. The only river
forecast point projected to go just into Minor flood stage is the
Dan River at South Boston. That may be a worst-case, and it would
take a greater amount of rain over a shorter period (more convective
rain rates) to increase the risk for minor flooding across the
forecast area. Given that confidence is low in flooding, a flood
watch has been issued at this time and would rather wait to see what
tonight`s rainfall brings before that is considered.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH/PM
NEAR TERM...AL/RAB
SHORT TERM...JH
LONG TERM...JH
AVIATION...AL/KK
HYDROLOGY...AL




...Update to aviation forecast discussion...



 .SHORT TERM...(This evening through Sunday)
Issued at 258 PM CST Sat Jan 21 2017

20Z water vapor imagery shows an upper level shortwave amplifying as
it moves across the southern Rockies towards the plains. At the
surface, a low pressure system is deepening over the southern high
plains in response to the shortwave. Weak ridging remained over
eastern KS.

For tonight models continue to take the bulk of the dynamics from
the shortwave aloft, mainly to the south of the forecast area.
However the model progs do show some weak forcing, moisture
advection and a diffluent pattern aloft developing over east central
KS this evening. So chances for rain showers this evening appear to
be improving. Although rain amounts will generally be around a tenth
of an inch. The bigger concern is the potential for dense fog to
form along the NEB state line late tonight. The RAP has been
consistent in developing dense fog over Brown and Nemaha counties
and this is supported by the ARW and NMM. Although this is dependent
on how far north mid level clouds advect north as models develop the
fog on the northern fringes of the cloud cover. Additionally surface
winds from the north are expected to freshen towards 12Z which
raises questions about how dense fog may be. Have included a mention
for areas of fog across northeast KS but uncertainty in visibilities
precludes any headline at this time. The next shifts can monitor
trends and reevaluate fog potential. Lows tonight should range from
the lower 30s north where skies may remain clearer longer, to the
lower 40s across east central KS expecting clouds to keep temps from
falling to far.

For Sunday, think skies should clear out by the afternoon as the
system south of the area continues moving east. Some low level cold
air advection is anticipated on the back side of the system so temps
should be cooler than today. Have highs in the lower 40s across
northeast KS where fog and stratus are possible to near 50 in
central KS.

.LONG TERM...(Sunday night through Saturday)
Issued at 258 PM CST Sat Jan 21 2017

Upper ridge building east into the Plains brings clearing skies
Sunday night. Warm air advection increases from the mid to the lower
levels late Monday into Monday night, though still dry through the
bulk of the troposphere so no precip anticipated. Models showing a
significant spread in handling upper energy moving into the central
portions of the CONUS Tuesday, but still keep the local area on the
dry side and precip chances limited, especially south of Interstate
70. Northwest winds behind this system late Tuesday into Tuesday
night brings much colder air in for Wednesday and on into the end of
the week as northwest to northwest flow dominates the column, though
airmass is still modified continental and keeps values near normal.
Will retain some mention of precip Tuesday night into Wednesday as
the trough axis moves through. Any of this appears light at the most
but would turn to wintry phases with time. Dry conditions should be
the rule beyond these periods.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 540 PM CST Sat Jan 21 2017

Light rain showers continue to push northward toward the TAF sites.
These have arrived at the Topeka terminals and should arrive at
within the hour. VFR conditions are expected to prevail at MHK. MVFR
visibilities are expected from 06-10Z at the Topeka terminals as
patchy fog develops within the scattered rain showers. Winds will
increase from the north at 10-15 knots by 15Z Sunday morning. As the
surface low moves southeast of the area, winds will begin to
decrease near the end of the period.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Baerg