Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/13/18
Area Forecast Discussion
National Weather Service Bismarck ND
917 PM CDT Wed Sep 12 2018
Issued at 917 PM CDT Wed Sep 12 2018
Convection began after 7 pm in southern Manitoba, and now has
developed southwestward into the Turtle Mountains and McHenry
County. Smaller cells developing southwest of that in the
Dickinson/Hettinger area. CAMs continue to show this northeast to
southwest arc for best chances of development, increasing in areal
coverage and intensity through around midnight/2 am cdt, then the
area of showers and thunderstorms moving eastward, finally exiting
the Turtle Mountains/Devils Lake Basin by around 3 am cdt.
The 00z Bismarck sounding indicated very unstable above the cool
surface layer, with strong southwesterly winds aloft creating decent
We collaborated with the Storm Prediction Center...and the thinking
is for chances of large hail late this evening when thunderstorms
are more isolated, then later tonight the hail threat should
decrease as storms congeal into lines. This is when the threat of
heavy rain over any locale is possible, as thunderstorms continue to
develop and move northeastward along the same lines (training
UPDATE Issued at 623 PM CDT Wed Sep 12 2018
Main concern for tonight is whether we will have initiation of
showers and thunderstorms before 10 pm cdt or not until after 9-10
pm. Latest iterations of CAMs indicating instability at mid levels,
and evidence of increasing mid level altocumulus clouds above the
cool surface layer. CAMs appear to hold off most of the convection
until the mid level shortwave energy impulses arrive in western ND
around 9-10 pm cdt. The surface warm front has lifted farther north,
entering southern ND where temperatures have reached the upper
80s/90F around Fort Yates/Oakes. The h925/h850 low level jet
continues to bring warm advection and increasing moisture northward
as per mesoscale analysis. So far we are capped above the cool
surface layer, but we think the frontogenesis expected with the
approaching mid level waves from the west should win out, resulting
in an outbreak of showers and thunderstorms, mainly southwest to
northeast - Dickinson to Minot/Rugby to the Turtle Mountains having
the best chances of measurable rainfall. The threat of strong to
possibly severe hail remains as well...likely quarter sized or less.
Latest CAMs indicate this round of showers to end in the Turtle
Mountains/Devils Lake Basin by 3-4 am cdt.
.SHORT TERM...(This evening through Thursday)
Issued at 130 PM CDT Wed Sep 12 2018
The main forecast issues in the short term period will be
thunderstorm chances and location, as well as aviation hazards.
Will discuss the Aviation hazards in the Aviation discussion
As far as convection tonight, it appears the threat for widespread
severe weather continues to diminish. We remain under an unstable
airmass aloft but the lower levels continue to remain capped south
of a northward lifting warm front, and quite cool north of the
warm front. If we would be able to generate convection, there
remains the potential for some hail, possibly up to quarter size,
but that appears to be the only main threat. The problem remains
that although we also remain in a broad southwest flow, there is
no strong trigger as the upper jet extends from southwest Montana
into central Manitoba with mostly channeled vorticity within this
region, and the entrance and exit regions also remain away from
the forecast area. CAMS are still hinting at enough forcing to
trigger some convection tonight but the number of CAMS indicating
strong convection over the area is decreasing. In addition,
earlier iterations of the CAMS were depicting convection farther
west into west central ND. This is also a trend that is becoming
less and less certain. Latest ESRL HRRR shows very little
convection over western and central ND tonight. The NSSL-WRF
depicts some convection over the north central around 02-06 UTC,
with the threat of hail confined to mainly the Turtle Mountains
area. We trended lower with pops tonight and limited the areal
extent of scattered to numerous showers and scattered
thunderstorms to mainly the east end of Lake Sakakawea to the
After midnight the convection quickly becomes limited to the far
north central, then tapers to just showers by 12UTC Thursday.
Thursday morning we kept some shower activity remaining from the
Turtle Mountains into the James River Valley. Later shifts may
need to look at extending pops into the afternoon over the JRV
into south central ND as steep lapse rates and and 2D fg forcing
remain, but synoptic forcing has moved east of this area so
confidence is not high at this time for adding light shower
activity to a previously dry forecast.
.LONG TERM...(Thursday night through Wednesday)
Issued at 130 PM CDT Wed Sep 12 2018
The forecast area remains within a broad southwest flow through
the upcoming weekend and into early next week. Temperatures will
remain fairly uniform, in the 60s north and 70s south. We may see
some lower to mid 80s along and south of the interstate Saturday
and Sunday, but then cool down into the 60s across the entire
forecast area early next week. With the aforementioned southwest
flow we can`t rule out a shower or thunderstorms at least
somewhere in the CWA each day, but overall precipitation chances
will be light. A stronger shortwave moves through the region
either Sunday afternoon (ECMWF) or Monday (GFS) and may bring
better chances of showers and thunderstorms, before possibly a
little quieter period develops as we head into the middle of next
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 623 PM CDT Wed Sep 12 2018
MVFR ceilings in stratus remain at KMOT to begin the 00Z TAF period.
Tonight look for showers and thunderstorms to develop mainly after
03z mainly from KDIK to KMOT with areas of MVFR to IFR ceilings and
visibilities. Late tonight precipitation will move east but MVFR to
IFR ceilings will spread south and east affecting KMOT-KDIK-KBIS-
KJMS Thursday morning. Moderate east to southeast flow this evening
will turn northerly tonight into Thursday morning from west to
Area Forecast Discussion
National Weather Service State College PA
1156 PM EDT Wed Sep 12 2018
A nearly stationary boundary over southeastern PA will be the
focus of showers right through Thursday and possibly into
Any impacts from Hurricane Florence will stay well to the south
of Pennsylvania through most or all of this weekend as a ridge
of high pressure noses into our area from the northeast.
The remnants of the Hurricane will track from the southern
Appalachians and Tennessee Valley toward Pennsylvania early next
week and could bring us periods of rain.
.NEAR TERM /THROUGH THURSDAY/...
Meso anal shows a weak inverted trough from northern NJ SWWD
through SERN PA down to just west of the Chesapeake. Just off
the surface the RAP shows a moisture axis associated with this
feature. Weak moisture convergence and marginal instability are
combining to support scattered showers and even an occasional
thunderstorm over my SERN zones within this region of weak
Earlier HRRR runs showed this activity staying pretty
disorganized over the SERN 1/3 of the CWA throughout the
evening. The latest run shows increasing shower activity after
1bout 3-4am from the Middle Susq Valley SWWD into Bedford and
Considering anomalously low FFG and high PWATS of 2 inches or
more across the far SE zones, we will have to stay alert for
localized flooding should the showers come to fruition and
become heavier and more persistent.
Overnight, other than the potential for convection, we included
the mention of fog and drizzle over the higher elevations
through Thursday morning.
Lows early Thursday will vary from the L60s up north...to the
upper 60s in the Susq Valley.
.SHORT TERM /THURSDAY NIGHT THROUGH 6 PM THURSDAY/...
It`s hard to see much clearing for Thursday but there should be
breaks. We could add a few deg F onto maxes for Thurs, putting
us at or even above normals for mid-Sept.
Expect to see a few areas of showers to develop mainly during
the midday and afternoon hours near some ill-defined boundaries
both at the surface an aloft. POP grids are in the chc to likely
category and certainly could be adjusted as confidence increases
in the timing and location of any distinct features that could
trigger the convection.
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Persistent east southeast flow remains the predominant weather
player on Thursday night and Friday with fairly robust deep layer
moisture across the region. Models and EFS continue to indicate at
least scattered coverage of showers with perhaps an isolated/brief
low-topped afternoon, with high temps near or slightly above normal
under the persistent east to southeast flow.
Latest track of Hurricane Florence is slightly farther south,
allowing for boundary layer drying later Friday and Saturday and
extending into Sunday. From here, solutions diverge dramatically
after Florence comes onshore (assuming it does so), with some new
solutions curving Florence remnants up the Appalachians and over
western PA in the Monday to Tuesday timeframe. Mornings on Sat and
Sunday may be gray with patchy drizzle, only for ceilings to lift
and allow afternoon sunny breaks, particularly across northern
PA as sprawling sfc high lies across the region. The wildcard
will be the trajectory of flow around the W-E oriented ridge
extending from central New England to Newfoundland, whose
extensive over-water fetch will combine with Florence`s
circulation to shunt western Atlantic moisture into the mid
Remnants of Florence may end up reaching the area Monday into
Tuesday with an increasing chance for showers and TSRA and bands of
locally heavy rain possible Monday through Tuesday. Should this
solution verify, a positive would be the forward speed of said
remnants getting caught up in freshening southwest flow, hopefully
minimizing the duration of heavier rain as Florence`s remnants whisk
through the region.
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Widespread IFR to MVFR cigs will continue across the region
through tonight and perhaps midday Thursday, before some drier
air from aloft and subsidence from high pressure ridging into
the region from the NE pokes some holes in the otherwise shallow
but extensive stratus/strato cu deck.
Areas of LIFR will develop across the western Mtns and even the
Lower Susq Valley airfields overnight and last until shortly
after daybreak before improving to IFR.
Hurricane Florence will impact the Carolinas through this
weekend. A high pressure area building into the region from the
north should advect a deep layer of drier air into much of PA
Sat/Sun with improving conditions.
Thu-Fri...Areas of AM fog/drizzle possible with low cigs and
mvfr visbys...then MVFR/VFR cigs. Scattered to numerous
showers. Isold PM tsra impacts possible.
Sat-Sun...Patchy AM fog/drizzle and low stratus cigs possible.
Mainly mvfr to vfr cigs both afternoons.
NEAR TERM...La Corte/Lambert
Area Forecast Discussion
National Weather Service Gray ME
1136 PM EDT Wed Sep 12 2018
A large ridge of high pressure will build and become centered over
the region through the weekend and into early next week. This
will bring dry weather and mild temperatures. The remnants of
Florence may bring some unsettled weather into the region next
.NEAR TERM /OVERNIGHT/...
Have adjusted precipitation chances in southern New Hampshire as
an area of showers associated with a weak wave moving through
southern New England will move through that area over the next
several hours. No other changes needed.
Temperatures look on track to fall into the lower 50s north to
lower 60s south tonight. Showers moving through the Berkshires
associated with a weak short wave will try to stay together into
southern NH later tonight. Current forecast has that covered
well. Clearing skies are allowing radiational fog to start
setting up, especially in valley locations. Fog tonight should
remain rather patchy though as drier air slowly works it`s way
into the region.
Nothing of significance to update so far this evening.
Temperatures look on track to fall into the 50s, with lower 60s
over southern NH. Radar indicates showers diminishing, but as
previous discussion mentions... there is another weak shortwave
that will swing through giving southern NH another chance for
precipitation tonight. Starting to see some decent clearing
already, so fog might be forming in favored areas before
High Impact Weather Potential: Minimal.
Pattern: Early afternoon surface analysis places building high
pressure over our forecast area as mid level heights continue to
build over eastern Canada. A cold front /more of a deep moisture
boundary/ has stalled across New England...with weak lift of a very
moist airmass to the south /PWATs near 2" per KCHH 12Z RAOB/ over
this boundary resulting in a slow moving area of showers and
embedded thunderstorms. As we move through the near term portion of
the forecast...heights aloft continue to build...with llevel flow
weakening and mid level flow gradually veering more westerly. This
will result in the aforementioned moisture plume being slowly pushed
south. Primary forecast concerns center around precipitation
chances and what degree of clearing can be realized as high pressure
continues to build from the north.
Through this evening: Showers continue over southern New
Hampshire...but have been weakening over the past hour as the
southern edge of the area of convection in southern New England
strengthens...robbing the northern area of inflow. This trend will
continue...with partly to mostly cloudy skies and temperatures in
the 60s at 8pm.
Tonight: Very slow evolution to the pattern as high pressure
gradually strengthens overhead with drier air slowly filtering
in from the north. One more vort lobe will ride along the front
overnight...likely helping maintain convective activity along
the front to our south. Some threat that the northern edge of
this activity brushes southern New Hampshire and have included
chance PoPs in this region. Current thinking...however...is more
in line with recent HRRR runs which suggest it will probably
remain dry. With very limited drying of the airmass and some
partial clearing...expect a good bit of fog development and have
included patchy wording throughout the entire forecast area.
Temperatures will not fall much given clouds and limited llevel
drying with lower 50s north and lower 60s south.
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
High Impact Weather Potential: Swell along the coast resulting
in high surf conditions. Otherwise...minimal.
Thursday: Deep-layer high pressure centered directly over the
northeastern United States for the day on Thursday with a wedge of
drier /PWATs below 1"/ air working in from the north. While
precipitation will have been pushed south of the region...thicker
clouds will likely still be impacting far southern portions of the
forecast area at daybreak...with clear skies to the north.
Drier air continues to gradually push south through the
day...however...and expect skies to turn mostly sunny even here.
Given impressive ridge overhead...deep mixing will be limited
and thus will likely not reach the full potential of T8s around
+13-14C. Keeping temperatures just shy of this mark...and closer
to fully mixed T9s would bring highs into the upper 70s to
right around 80...in good agreement with consensus guidance.
Thursday Night: Not much change in the pattern through Thursday
night with deep moisture kept at bay south and west of the region
given strong ridge overhead. One small change is the trajectory of
the low level flow which shifts from more northerly on Thursday to
more easterly overnight...with an increasing marine source to the
air...particularly over the southern half of the forecast area. The
airmass is not particularly dry to begin with...with dewpoints in
the mid/upper 50s...and thus do not expect temperatures to fall too
lower during the overnight /50s-lower 60s/. This added low level
moisture brings the threat for fog...and possibly low stratus
near the coast. Will not go too far with cloud cover in this
forecast package but will add mention of fog throughout the
High Surf: Long period /at least 13 second/ swell of 5-6 feet
looks to continue through Thursday night /and possibly into
Friday/. For this reason...and in collaboration with BOX/CAR
have hoisted a high surf advisory for Thursday and Thursday
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
A high amplitude blocking ridge of high pressure will continue
to build and become centered over the northeast through the
weekend and into early next week. This will provide a good
amount of sun during the day and mostly clear nights. Patchy
valley fog each night can be expected. Temps will be very
comfortable with highs generally in the upper 70s to lower 80s
and lows in the mid 50s to lower 60s.
Models indicate moisture from the remnants of Florence should
lift north early next week, bringing rain to New England by
around Tuesday. The northern stream with its westerly flow will
quickly pick up this system and move it rapidly northeast.
Although some brief heavy rainfall may occur as it quickly moves
northeast, no significant problems are expected at this time.
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Summary: High pressure over northern New England will gradually
strengthen and build south through Thursday night pushing rainfall
south of the region with dry weather Thursday and Thursday night.
Restrictions: Highly variable conditions at the moment with some VFR
conditions beginning to appear over northern/eastern areas
while conditions have deteriorated to IFR over our southern
terminals. A band of showers will impact southern
NH/southwestern ME through this afternoon with continued IFR
restrictions. Tonight...while clearing will push from north to
south...fog development is expected...with LIFR/IFR conditions
likely at the terminals especially after midnight.
Improvement to VFR is expected on Thursday with a good chance for
low stratus and fog development Thursday night.
Winds: Winds will be light through the period...northeasterly around
5kts today...becoming calm/light-variable tonight and light
southeasterly around 5kts for the day Thursday before again going
calm Thursday night.
LLWS: No LLWS expected through Thursday night.
Lightning: Very low threat of lightning for MHT/CON/PSM through 00Z
this evening then no lightning expected beyond this through Thursday
Long Term...VFR except local IFR conditions 06z-13z in areas of patchy
valley fog each night.
Short Term...SCAs for seas continue through at least Thursday
in the form of 4-7` long period swell. Some potential that we/ll
need to extend this through Thursday night for at least a
portion of the outer waters...but would like to see how things
evolve with Florence to make any future changes.
Long Term...Winds and seas expected to remain below SCA criteria
through the period. Some long period swells may still affect the outer waters.
ME...High Surf Advisory until midnight EDT Thursday night for
NH...High Surf Advisory until midnight EDT Thursday night for
MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT
Thursday for ANZ150-152-154.
NEAR TERM UPDATe...Kimble
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
939 PM CDT Wed Sep 12 2018
930 PM CDT
No major changes to the forecast theme overnight into Thursday
morning. There is an area of stratus/stratocumulus in the
3500-4500 foot range over north central Indiana. Low level flow in
this cloud layer is from the east, and with the shifting ridge
axis, flow is turning more southeast. Some of this cloud is
eroding on the leading edge due to slightly drier air farther
westward. Still, RAP guidance does still suggest that some of this
cloud will get into NW Indiana and at least portions of NE
Illinois. The westward extent will be limited, but expect where it
does reach to be of the scattered to briefly broken nature
overnight and into the morning as temperatures cool.
208 PM CDT
Quiet, dry weather is expected for the short term forecast period.
A ridge of high pressure will remain parked over the region. The
main concerns for the period will be how far inland a lake breeze
will penetrate and the potential for some patchy fog and increasing
cloud cover spreading from southeast to northwest during the morning
hours. A weak lake breeze is still trying to push inland. Winds
along the lake front have turning onshore causing temperatures to
drop off into the low 70s. Inland, under ample sunshine,
temperatures are rising into the lower 80s. Expect that the few-sct
stratocu that has been able to develop will dissipate at sunset,
leaving clear skies into the overnight hours. With time overnight,
expect that the cloudiness over the Ohio Valley and ern Indiana will
be shunted to the northwest as the sfc ridge extending from New
England to the Lower Mississippi Valley gets squeezed some as
Hurricane Florence pushes westward and low pressure and an
associated cold front push across the Northern Plains. The main
impact of the increasing cloud cover will mostly be on overnight low
temps and highs tomorrow. In the absence of this cloud cover, would
have expected another day much like the past couple, with highs
mainly in the low 80s and lake breeze cooling along the lake front.
However, the increasing cloud cover could keep min temps tonight a
little higher and max temps tomorrow a little lower. So, have gone
with highs tomorrow in the middle to upper 70s, expect lower 70s
close to the lake. However, should the cloud cover thin out and
become a bit less opaque, temperatures could have the potential be a
little higher. In either case, no pcpn is expected.
208 PM CDT
Thursday night through Wednesday...
Tranquil weather will continue into early next week with persistent
blocking from ridging across the Great Lakes and Hurricane Florence.
Given the antecedent dry air mass and lack of appreciable forcing,
conditions should remain dry across the area. Max temps in the low
to mid 80s inland (6-9F above normal for mid-September) and the mid
to upper 70s along Lake Michigan are expected.
A trough over the Pacific NW this weekend should pick up the
remnants of Florence across the Ohio Valley early to mid next week,
keeping its associated precip east of the CWA. Guidance varies on
the timing of the passage of a cold front trailing the trough. With
the main mid-level energy lifting NE across the far northern Great
Lakes, a slow-moving front with sparse precip is expected to cross
the CWA sometime from Tuesday afternoon through Wednesday night. A
later arrival is favored, with the front possibly in the process of
stalling/washing out over the area.
For the 00Z TAFs...
Surface ridge axis will remain over the region through the TAF
period resulting in fairly steady state conditions. Expect light
southeast flow, except for a shift to the east or northeast midday
Thursday with passage of a lake breeze. A couple other minor
concerns to address... there could be some patchy ground fog
overnight, mainly at DPA and RFD. Don`t have a lot of confidence
in how widespread this will be or how much it will impact
visibility, so opted to not make any changes with the tempo, but
something to keep an eye on overnight. Finally, VFR stratus deck
(035-040) over northeast Indiana may expand west across the
Chicago area terminals overnight and lower to or near MVFR (030).
If this occurs, there may be a few hours during the predawn and
early morning hours Thursday with MVFR ceilings before conditions
improve back to VFR diurnally. Not including a BKN MVFR deck in
the TAFs yet as guidance remains mixed to whether or not this
will occur, but another consideration to keep in mind overnight.
208 PM CDT
A ridge of high pressure extending westward from New England across
the Great Lakes region will persist into early next week. This will
allow winds to remain generally from the SE quadrant at less than 20
knots through the period. The strongest winds during the period are
expected through this evening across the north half of the lake,
where S winds to 25 knots are possible.
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Area Forecast Discussion
National Weather Service Memphis TN
935 PM CDT Wed Sep 12 2018
Updated to lower evening rain chances
Radar trends show only a few sprinkles left across the Midsouth
under what has been a three-day fetch of midlevel moisture.
Have replaced the chance for rainshowers tonight...to just
isolated sprinkles through midnight. Cloud cover will continue
beyond that time frame...with more peaks of sun expected during
the day Thursday. All other evening forecast parameters are
currently on track.
.PREV DISCUSSION... /issued 637 PM CDT Wed Sep 12 2018/
Updated to include 00Z aviation discussion.
.PREV DISCUSSION... /issued 322 PM CDT Wed Sep 12 2018/
Temperatures across the Midsouth vary significantly, ranging from
the upper 80s in Northeast Mississippi to the middle 70s in
Northeast Arkansas where clouds have limited insolation. A few
sprinkles have been observed across East Arkansas, the Missouri
bootheel as well as West Tennessee, generally along and North of
Interstate 40. Some of the rain observed on radar is probably not
reaching the ground as it is falling through a fairly dry
airmass...from a cloud deck of 8-10,000 feet. Surface dew point
depressions are generally 10-15 degrees F. Most of North
Mississippi has been dry. The HRRR seems to have had a good handle
on the precipitation today so will continue to follow its
guidance this evening and overnight. Will keep light rain going
through Midnight for much of the area with the exception of
Northeast Mississippi. Overnight lows should fall into the low to
Tomorrow and the next several days should be dry. All eyes are on
Hurricane Florence. It is not expected to have any direct impact
on the Midsouth...although subsidence outside of its direct impact
of wind and rain could actually help to keep us dry. Temperatures
tomorrow should rebound into the middle to upper 80s across most
of the Midsouth with upper 80s expected area wide Friday and over
A strong ridge over the Midsouth may begin to break down early
next week resulting in slightly cooler temperatures. However,
with such a powerful system in Florence at play, forecast
confidence is low into early next week. For now, we will stick
with dry conditions and near normal temperatures.
00Z TAF Set
VFR conds expected over next 24 hours. The exception will be some
light MVFR fog and CIGs at MKL near sunrise. Winds will be from
the northeast 5-9 kts through the period.
Area Forecast Discussion
National Weather Service Medford OR
747 PM PDT Wed Sep 12 2018
Showers and a few thunderstorms have popped up over the last few
hours. Right now, as of 740pm , we have counted above 4 cloud to
ground strikes. Radar suggests these showers are losing access to
instability in the region. The other notable feature are all the
showers in northern California. These should be heading east of
the Cascades this evening into the overnight hours.
The only other change to the forecast was adding smoke back in for
some locations near the Klondike and Delta fires. The eastern
part of the Klondike fire did see some rain, but the north western
part of the fire likely didn`t see enough to really impact smoke
production tomorrow. Therefore, Grants Pass and most portions of
Josephine county should see smoke tomorrow into the evening hours.
It`s difficult to say how low visibilities will be, but they
should be below 6 miles giving what the HRRR Smoke model is
showing. Read the discussion below for more information beyond
.AVIATION...For the 13/00Z TAFs...Mostly VFR conditions
exist late this afternoon, with some mountain obscuration likely in
the Coast Range. Isolated to scattered showers are expected west of
the Cascades in the Coast Range and north of the Umpqua Divide
through this evening. Areas of MVFR are expected to redevelop in
this same area late this evening through Thursday morning, though an
incoming cloud deck around 5,000 feet AGL may disrupt the formation
of these areas of lower clouds in all or part of this area. Any MVFR
ceilings that do form overnight will improve to VFR by late Thursday
morning or early afternoon.
There is a slight possibility of thunderstorms this evening from
just east of the Coast Range, along and north of the Umpqua Divide,
eastward into northern Klamath county.
Elsewhere, east of the Coast Range, south of the Umpqua Divide, and
from the Cascades eastward isolated showers with mainly VFR ceilings
are possible later this afternoon into the evening. Late tonight
into early Thursday morning patchy fog and MVFR to IFR low clouds
will be possible for these same areas, especially in areas that do
receive rainfall. Any restrictions to CIG/VIS should be brief,
before returning to VFR.
Partial terrain obscurations should continue across the mountains
through this evening, with the greatest obscurations from the Oregon
Cascades and Siskiyous westward.
.MARINE...Updated 200 PM PDT Wednesday, 12 September 2018...
An upper level trough is expected to remain over the Pacific
Northwest the rest of this week and through this weekend bringing
with it a series of weak cold fronts. Winds and seas are expected to
remain generally light through weekend. The strongest of the weak
fronts is expected Saturday night into Sunday morning when southerly
winds in the vicinity of Cape Blanco northward could reach sustained
values of 15 to 20 knots. Northerly winds and wind wave dominated
seas are expected to return on Monday with advisory level conditions
possible south of Cape Blanco beginning late Monday or early
.FIRE WEATHER...Updated 200 PM PDT Wednesday 12 September 2018...
No critical fire weather conditions are expected through early
next week. However, there will be gusty winds east of the Cascades
Friday afternoon and evening and again Saturday afternoon and
evening. These winds will be associated with a front that will
move onshore this weekend. It will bring more widespread
precipitation to the area, but not season-ending rains.
.PREV DISCUSSION... /Issued 454 PM PDT Wed Sep 12 2018/
Updated aviation discussion.
DISCUSSION...Isolated to scattered showers are beginning to
develop just inland from the coast to about Interstate 5 near and
west of Roseburg. In fact, the most recent observation from the
Roseburg airport was showing 4SM and light rain. Expect these
showers to expand in coverage, mainly over inland areas through
this evening, though showers may also move into the coastal
waters from the north and west. There have been a handful of
lightning strikes north of the area (from Lincoln City northward)
this afternoon where better instability is located, but this area
will shift across the area late this afternoon and early this
evening, so cannot rule out an isolated thunderstorm, especially
north of the Umpqua Divide.
The upper trough and the associated short wave disturbance
responsible for the showers will move onshore tonight into
Thursday morning. The GFS, NAM12 and the convection allowing
models continue to show an area of showers breaking out near
Mount Shasta and the Medicine Lake region this evening, then
expanding out toward the northeast across SE Klamath, NW Modoc
and Lake Counties overnight into Thursday morning. We have
increased the coverage here and although many areas could still
miss out on rain, some areas may receive wetting rainfall. This
will be a quick-moving system, so any showers left over the east
side Thursday morning should quickly exit the area to the east.
The increased cloud cover over there tonight should preclude frost
development. It will be a race though as skies try to clear in
some areas toward morning allowing temperatures to dip into the
mid 30s. We didn`t issue a frost advisory for this reason, but if
you do have sensitive vegetation, it still may be a good idea to
We`ll be between systems Thursday into Friday as the long wave
trough more/less elongates to the southwest just offshore. So,
shower chances diminish during this time frame, but there still
could be isolated activity over the coastal waters, along the
coast north of Cape Blanco and over the lower Umpqua Valley. There
will be enough clearing over the east side Thursday night, for
temperatures to fall back to near or below freezing. A freeze
watch was issued for that potential and can be viewed at NPWMFR.
Another disturbance will dig southward from British Columbia this
weekend. Models are showing a lead short wave ejecting out across
northern California Saturday and across SE portions of our CWA by
Saturday evening. But, primarily due to a lack of moisture,
guidance is not really generating any precipitation with it.
The focus for precipitation will be with the disturbance digging
into the area from the north. Models are in fairly good agreement
showing this system moving onshore Saturday night, then pushing
inland on Sunday. Right now, the GFS is a bit deeper with the
trough than the ECMWF, but curiously, the ECMWF is more bullish
with precipitation farther to the south. We`ve split the
difference here with high chance to likely POPs along the coast
north of Gold Beach and into the Umpqua Valley. Precipitation
probably won`t get much south and east of these areas, but we have
a slight chance of showers down to the Siskiyous and over to the
Cascades. Overall, temperatures will remain about 5-10 degrees
below normal through Sunday. Then, after the long wave trough
lifts out, temperatures should get back closer to normal by early
OR...Freeze Watch from late Thursday night through Friday morning for
CA...Freeze Watch from late Thursday night through Friday morning for
Pacific Coastal Waters...None.
Area Forecast Discussion
National Weather Service Blacksburg VA
738 PM EDT Wed Sep 12 2018
A lingering frontal boundary and weak wedge of high pressure
will combine to keep some showers and thunderstorms across the
Appalachians and central mid Atlantic region through tonight.
Showers from hurricane Florence will begin to push into the
region from the east by Thursday night, with additional heavy
rainfall and gusty winds expected through the weekend and into
the first part of next week.
.NEAR TERM /THROUGH THURSDAY/...
As of 738 PM EDT Wednesday...
Decreased pops for this evening into tonight. Added some fog
overnight into Thursday morning. Adjusted temperatures with the
latest surface obs, their trend and leaned towards GLAMP. More
changes later tonight.
As of 245 PM EDT Wednesday...
Weakness in the wedge have allowed scattered
showers/thunderstorms to develop. Our airmass remains quite
moist with precipitable water values approaching 2 inches, so
locally heavy downpours can be expected. While some localized
flooding is still possible, indications are that activity will
remain scattered enough to preclude the necessity of a watch
issuance. Will handle convective activity with short fuse
statements. Showers may cluster along the length of the Blue
Ridge overnight before dissipating so will hold on to higher
POPs down the Ridge later before trending down. Low clouds and
fog will blossom again toward morning with dense fog at some
locations, with another round of poor conditions along I77
through Fancy Gap expected.
Low clouds/fog will dissipate Thursday morning and allow for
some breaks of sun as we get into a little bit of subsidence
along the periphery of Florence late morning/early afternoon,
but the initial effects of the hurricane will start to be felt
as showers start to rotate around the large circulation and move
into the region from the east/northeast late in the day across
far eastern portions of the piedmont.
Lows tonight will generally be around 70 east of the Blue Ridge
with middle 60s to the west. Highs tomorrow will be in the lower
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 330 PM Wednesday...
Forecast for the weekend and into early next week is contingent
on the eventual track of Hurricane Florence and its remnants at
that time. Trends for the system continue to delay the onset of
the heaviest precipitation for southwestern VA and southeast WV
with primary impacts Friday and Saturday to the Carolinas. This
does not make us immune to some of the impacts, as we will
begin to see an increase in wind speeds across the Piedmont and
into the higher elevations along the Blue Ridge Parkway. Wind
gusts of 25 to 40 mph will become common along the Parkway where
the ridgeline is exposed to the increasing upper level winds.
Winds across the Piedmont will also freshen-up as the pressure
gradient increases between the cyclone and the area of high
pressure to our north. Outer rainbands from the system will
rotate into the area from the southeast later Friday and Friday
night. Once the system makes landfall and begins to weaken these
rainbands may extend outward to encompass parts of, if not the
entire CWA. There will also be areas of subsidence between the
bands where little or no rain occurs. This makes it difficult
with respect to the forecast timing other than to advertise
showers as opposed to an all out rain.
Temperatures will trend downward over the weekend as cloud cover
expands across the forecast area...readings getting no warmer
than the 70s.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 330 PM EDT Wednesday...
An opportunity for an extended period of rain exists for Sunday
through Tuesday. Forecast details remain contingent on the
track of the hurricane remnants, but at some point in time,
whether its Sunday or Monday, the system should become
extratropical and get caught up in the mid-latitude westerlies
and drawn northward. This will then focus the heavier rains
farther north along the spine of the Appalachians and this is
when it will be "game-on" with respect to the heavier rains for
our forecast area. The advertised 5 to 15 inch rainfall amounts,
with respect to event totals, are still on the table and should
not be ignored with respect to local emergency preparations.
Flood producing rains still appear likely. The difference to
previous forecasts is with respect to timing.
Once the system weakens and gets drawn northward, winds should
remain below tropical storm levels. In spite of the weakening
wind field, rainfall will saturate the ground increasing the
risk for falling trees and potential for power outages.
Looking past Tuesday, the flow is forecast to be zonal. A mid
latitude front may tease the area mid-week with some temporary
drying, but flow pattern does not suggest in big changes on the
horizon with respect to temperatures.
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 738 PM EDT Wednesday...
SCT to BKN MVFR clouds this evening into tonight. A few showers
are possible early tonight. Shaped the pops this evening
towards the HRRR and NAM with less areal coverage. CIGS will
trend down to IFR/LIFR by daybreak with some patchy dense fog
particularly at KBCB. Expect sites will trend to MVFR by
mid/late Thursday morning with any shower/thunderstorm
development late in the period confined to the far east and out
of TAF sites.
Winds will generally be light but will start to increase toward
the end of the valid period and become a bit gusty especially
across eastern portions of the piedmont.
High confidence in downward trend to IFR/LIFR overnight.
May see overall VFR return Thursday pending the timing of
Florence with much of the region still west of this system until
late week. Sub-VFR appears likely on Friday with Florence
across coastal southeast North Carolina based on the latest
track from the National Hurricane Center. With Florence now
expected to drift west toward the western Carolinas this
weekend...a delay in rain bands associated with the hurricane
could occur with heavier rainfall perhaps staying south of most
of the terminals into Sunday.
Confidence is medium for all elements into Wednesday, but
gradually transitions to below average confidence by Thursday
into/through Sunday due to existing uncertainties associated
with the movement and placement of Florence.
As of 400 PM Wednesday...
Potential still exists for a major hydrologic event. What can
be said with assurance at this juncture is that timing will be
delayed due to the system slowing and making a southward track
prior to moving northward early next week.
Antecedent conditions...streams are above the seasonal norm.
Output from the National Water Model shows nearly all our
streams and rivers running at above to much above normal flows
for this time of year and a similar condition is evident on the
USGS Waterwatch website. Admittedly, those normal flows are near
their annual minima in early to mid-September but with the
rainfall projected on the consensus of models, moderate to major
flooding within several river basins is not out of the
question. In fact, antecedent conditions may not matter that
much if we get enough rain. The other concern is the
possibility of landslides.