Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/01/17
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKDT Thu Aug 31 2017
.ANALYSIS AND UPPER LEVELS...
Two upper level lows dominate the weather across the mainland with
one low just south of the Seward Peninsula, and a second low over
Kodiak Island. While the upper low near the Seward Peninsula is
supporting light scattered showers across the Kuskokwim Delta.
Across Southcentral, there is much more low level support for
widespread showers with the remnants of a front, along with broad
onshore and upslope flow. The afternoon sounding indicates fairly
steep lapse rates and a saturated atmosphere, which is likely
allowing for some spillover precipitation currently and preventing
completely dry conditions in downslope areas. Meanwhile, fairly
dry conditions persist across the Bering with broad northerly
The NAM remains the model of choice for both the east and west
domains and models are in good agreement in the short term for
synoptic conditions. The NAM and WRF are particularly doing a
good job of capturing the gap winds through the Alaska Peninsula
and associated mountain wave dynamics. The HRRR is capturing the
low level convergent winds well and is therefore capturing the
rain showers over Anchorage this afternoon.
PANC...VFR conditions will persist even as light showers continue
to fall into the evening hours. While strengthening down inlet
flow has bent the surface southeasterly Turnagain arm winds away
from PANC with light northwesterly surface winds taking over, wind
shear may still be a concern on the approaches and departures.
Southeast surface winds are likely to push back in to PANC late
afternoon through the evening.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Rain showers will continue across the gulf coast and Susitna
Valley through the majority of the overnight hours. In the
meantime, cross barrier flow over the Chugach Mountains will
weaken and allow for scattered showers to develop across Anchorage
and the Matanuska Valley. By Friday morning, a combination of
southeasterly winds out of Turnagain Arm will combine with
southwesterly winds in Cook Inlet (up-Inlet flow) to create a
convergent boundary over west Anchorage. Models are struggling on
where the mesoscale banding will set up as the NAM and GEM show a
negatively tilted upper level axis which would push the banding
west of Fire Island. Regardless, early Friday morning looks wet
with the potential that the morning hours could see steady light
to moderate rainfall.
A rapidly developing low pressure system will develop south of
the Alaska Peninsula Saturday morning and quickly push a gale
force front into the western gulf by Saturday afternoon. This
front is expected to bring moderate to heavy rainfall to Kodiak
Island and the gulf coast through the weekend. However, interior
locations will remain largely on the dry side as impressive cross
barrier flow (35-50 kts) should downslope much of the precipitation
as it interacts with the coastal mountains.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level low centered over Bristol Bay, which is embedded
within a longwave trough covering most of mainland Alaska, is
bringing widespread cloud cover and rain to Southwest Alaska east
of Bethel. This system will slowly move east bringing a quick
break in the precipitation overnight into tomorrow. Cooler air
filtering down from the north on the backside of this system
combined with partial clearing will allow temperatures to dip
below 40 degrees for most locations tomorrow morning, with low to
mid 30`s expected for locations in the Kuskokwim River Valley.
Another upper level low swings down the coast by Friday evening
bringing another round of steady rain for the area starting in
the Y-K Delta Friday night and spreading east and south through
the day on Saturday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Strong northerly flow over the eastern Bering will begin to taper
off tonight, though wind gusts may still reach gale force coming
out of channeled terrain on the Pacific side of the eastern
Aleutians and southern AKPEN.
A major change in the overall pattern will begin to take shape
tomorrow as a low over Kamchatka will move east into the Bering
Sea by the afternoon. At the same time, a surface low will form to
the south of the Western Aleutians and remnants from former
Typhoon Sanvu will get pulled up into a strong North Pacific jet
stream and ejected northeast towards the island chain. Models are
showing these three systems merging together by Saturday night
into a rapidly intensifying low pressure system about 250 miles
southeast of Cold Bay. A strong 175 kt jet streak will aid in
developing this system into a well developed extra-tropical
cyclone by Sunday, with all models showing the surface pressure
bottoming out at or below 970 mb on Sunday afternoon. Previous
model runs were inconsistent with the low placement and track but
seem to be coming into better agreement, at least through Sunday.
Impacts from this system will be heavy rain along most of the
central and eastern Island chain aided by upslope flow. Winds will
also be very strong but, due to the distance of the low center
from the AKPEN and warm air advecting up from the south, we are
not expecting this to be a storm force low with sustained winds
remaining below 48 kts across a majority of the area. Large swells
are expected though, with long fetch southerly winds leading to
seas above 20 ft for open water locations south of the AKPEN and
southwest of Kodiak.
.LONG TERM FORECAST (Days 3 through 7)...
The big question going into next week is what will happen with the
rapidly intensifying low south of the Aleutians. Depending on how
far south the trough digs it may tap into tropical moisture and
bring a long fetch of moisture to southern Alaska. Most current
operational runs and ensembles are indicating this to be the case
which would mean Monday and Tuesday would see steady, heavy rain,
primarily along the north Gulf coast. However, there are still
differences in where the low will setup and the trough may not dig
far enough south.
SYNOPSIS AND MODEL DISCUSSION...ELN/JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
Area Forecast Discussion
National Weather Service Wakefield VA
916 PM EDT Thu Aug 31 2017
A cold front will drop across the area late tonight, becoming
stalled across North Carolina on Friday. The remnants of Harvey
will shunt tropical moisture along the boundary, lifting it back
north as a warm front Friday night through Saturday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
9 PM Update...Afternoon forecast handling things pretty well.
Have made a few adjustments to POPs/Wx across NE NC where
persistent showers have been more widespread than earlier
thought. These showers are trending toward the coast, and look
to be offshore before 03Z. Attention then turns to moisture
trying to move northward ahead of the remnants of Harvey. Hi-res
models have been inconsistent the last few runs regarding how
quickly significant precip comes northward. Surge has been
inhibited the last few hours by significant tstm development now
exiting the Carolinas/GA coastline. So, current forecast of
gradual increase in POPs after 06Z looks good and have not made
changes after that time.
One aspect of the precipitation that will need to be monitored
is the suggestion from recent HRR runs that showers/tstms fire
after 06Z as cold front reaches deeper moisture over SE VA/NE
NC. This not covered well in afternoon forecast, and will
monitor for another hour, and see if this trend persists before
Temps appear on track as most cooling expected late tonight
after cold frontal passage.
...Previous Discussion...Latest weather analysis features weak
high pressure in places along/just offshore of the Mid- Atlantic
coast. To the north, a strong sfc cold front continued to drop
across the northeast and Ohio River Valley toward the Mid-
Atlantic region. Meanwhile, to the South, T.D. Harvey was
located over the lower Miss Valley, sliding NE toward the mid-
Radar coverage has been quite light today, owing to weak forcing
and dry mid-levels. Accordingly have dropped off pops a bit
across much of the area through early evening. Slow increase in
sky cover continues late this aftn into this evening, as better
slug of overrunning moisture/WAA arrives from the SW out ahead
of the lead shortwave from Harvey`s remnants. Pops will bump
into 30-50% range south, 20% central VA. Given increasing PW
values and likelihood of numerous weak disturbances pushing
through, will go with areal coverage (iso-sct) wording through
the night. Time-lagged HRRR and RAP are in general agreement of
this solution through midnight. Showers become likely late
along and south of the US-58 corridor. Lows ranging through the
60s to near 70 SE.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Weak cold front will drop down acrs the region early Fri
morning, before becoming stalled south of the area
acrs NC on Fri. Meanwhile, low pressure from the then post-
tropical remnants of Harvey will lift NE fm nrn MS northeast
into cntrl KY tonight into Sat morning, eventually lifting up
into the northeast and getting absorbed into NE CONUS upper
trough finally being shunted offshore late in the weekend.
Overall, 12z models continue with a flatter and relatively
progressive solution, with the lead shortwave and onset of
rainfall. First batch of showers push offshore in the morning,
before showers become more widespread from the late morning into
Friday night, as increasing overrunning moisture pushes across
the area as high. POP remains in likely range Fri morning (SW),
before spreading NE across the rest of the local area into Fri
aftn and evening. Most widespread rainfall looks to be later Fri
aftn thru Sat morning, with rain potentially tapering off a bit
quicker acrs the west on Sat. morning, as nose of mid- level
drying nudges back in from the southwest. QPF in the 1.0 to
2.0" range likely acrs the region thru Sat night. Highs will
range fm the lower to mid 60s NW, to the lower to mid 70s SE VA
and NE NC on Fri, moderating a bit back closer to normal on Sat
into the 70s to lower 80s.
Concerned for potential for some clearing in the warm sector
behind the system Saturday aftn. In the event of some partial
clearing, weakening/sheared out remnants of Harvey along with
veering low- level flow could provide enough support for
isolated to scattered convection. Area of concern is across SE
VA/NE NC, where a marginal risk remains in place. Highs in the
70s to low 80s across the SE.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Overall, the GFS and the ECMWF are in pretty good agreement with the
overall synoptic pattern from Sunday through Thursday. Both models
show the low pressure system associated with the remnants of Harvey
pulling away from the coast on Sunday morning and high pressure
building into the region by Sunday night. The GFS is a little slower
than the GFS and NAM and would suggest that there is still a chance
for some shower as the upper trough cross the Delmarva. So have
kept a slight chance of shower through midday for the upper trough
passage. Temperatures should Sunday afternoon should be in the upper
70s to lower 80s
Behind the trough, upper level ridging returns with the surface
high. This high slowly retreats to the NE from Monday into Tuesday
night, while providing dry weather through that period. Expect a
slow warm up in temperatures with readings in the low to mid 80s
Monday and mid to upper 80s on Tuesday.
The next cold front will arrive later Tues night into Thursday.
Ahead of this front, the models continue to show a good tropical
plume of moisture sliding northward into the Mid-Atlantic states.
This additional moisture could lead to some heavier showers as the
front slowly moves into the region. With the cloudy conditions
expect cooler temperatures in the 70s and depending on the size and
extent of the rain shield, could even see readings maybe only in the
From Thursday forward however the models diverge pretty dramatically
as far as will the front move through the area like the GFS or stall
and retrograde like the ECMWF. Some of this is also a factor in how
the model deals with Irma and its approach, which the models are
very different in handling. For now, have gone with a little more
of a blend of the solutions and kept the front stalled along the
coast on Thursday, keeping the chance for showers ongoing, but
confidence at this point in time is much lower than the forecast for
Sunday through Wednesday.
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR conditions conditions are expected through the first half of the
night to start the forecast period. A stray shower or thunderstorm
also cannot be ruled out overnight at ECG/ORF/PHF. MVFR ceilings and
the threat for more widespread showers works in from the south by
Friday morning. Expecting widespread MVFR to potentially IFR
ceilings at all of the southern TAF sites, ECG/ORF/PHF, Friday
morning lasting through the remainder of the forecast period. Sub-
VFR conditions and showers will be possible at RIC by Friday
afternoon. A cold front will drop across the region late tonight
into early Friday with winds veering to the north/northwest
Outlook: Sub-VFR conditions will be likely at all TAF sites late
Friday through Saturday as moisture from Harvey pushes across a
stalled frontal boundary. Dry weather and VFR conditions are
expected Sunday afternoon through Monday as high pressure builds
into the region.
Latest surface analysis centers high pressure offshore the Southeast
coast with tropical depression Harvey located over the lower
Mississippi River Valley. A cold front was stretching from the Upper
Midwest eastward into the Northeast. Flow remains light and variable
over the waters, generally at or below 10 knots. Seas have subsided
to 2-4 feet. Waves 1-2 feet. The front drops over the waters late
tonight into early Thursday morning as the remnant low of Harvey
lifts over the Tennessee Valley. The pressure gradient strengthens
as high pressure builds over the Great Lakes. As a result, a post
frontal surge of north to northeast winds to ~20 knots with gusts of
25 to 30 knots is expected late tonight into Friday morning. Waves
build to 2-4 feet and coastal seas again build back to 4-6 feet late
tonight/early Friday morning. Only changes made to headlines in the
Bay was to extend the upper Bay through early afternoon before high
pressure builds southward over the waters. Have raised SCA headlines
for the coastal waters, first north of Cape Charles Light late
tonight, then south of Cape Charles Light mid morning Friday as seas
build to 4-5 feet. The front stalls in the vicinity of northeast
North Carolina Friday as the weakening remnant low of Harvey lifts
into the Ohio Valley. High pressure extends off the Northeast coast
Friday, as flow becomes more easterly with speeds around 15-20 knots
in the lower Bay and southern coastal waters. Seas subside below 5
feet in the north Friday, but remain 4-5 feet in the south. Waves in
the mouth of the bay 3-4 feet. Guidance still struggling to handle
the frontal boundary Saturday as low pressure dissipates over the
Ohio Valley. Based on the uncertainty, have held off on extending
the SCA headlines into Saturday, but SCA conditions appear likely
back in the upper Bay and northern coastal waters by Saturday
afternoon as the gradient winds lift northward. Low pressure
develops over the Mid-Atlantic Saturday night as a trailing cold
front pushes across the waters. Conditions improve Sunday through
early next week as high pressure builds in from the west.
Water levels remain elevated in the upper Bay this afternoon, but
are subsiding to around 1 foot. Additional minor flooding is not
anticipated, but a coastal flood statement may be needed for
Bishop`s Head as it will approach minor flooding during high tide
this evening. Water levels will creep back upwards of 1 to 1.5
feet this weekend as a period of onshore flow is expected Friday
through Saturday. Water levels will approach minor flooding
thresholds in the Bay Friday and Saturday.
Have kept the high risk for RIP currents Friday for Virginia
Beach southward to the Outer Banks for shorebreak of 3-4 feet,
shore normal wave directions, and northeast winds. Have lowered
the Eastern Shore beaches to moderate risk for RIPs.
Very cool temperatures expected on Friday (Sep 1st). Record low
maximum values may be challenged. One thing to note is that
official climate is from 12am LST to 12 am LST (1am EDT-1am EDT)
for the calendar date. Fri still appears to be a scenario in
which the daily high occurs late tonight (* 1am EDT) with
falling temperatures through the rest of the day. In that case,
a record low max may not be set even if readings during the late
morning and afternoon are below the record vales. The record
low max data for Sep 1st is listed below for reference.
* Richmond: 68 (1928)
* Norfolk: 71 (1915)
* Salisbury: 69 (2006)
* Elizabeth City: 70 (1967)
MARINE...Small Craft Advisory from 4 AM Friday to 6 AM EDT Saturday for
Small Craft Advisory from 10 AM to 7 PM EDT Friday for ANZ633.
Small Craft Advisory from 1 AM to 1 PM EDT Friday for ANZ630-
Small Craft Advisory from 7 AM to 1 PM EDT Friday for ANZ638.
Small Craft Advisory from 4 AM to 4 PM EDT Friday for ANZ650-
Small Craft Advisory from 10 AM Friday to 6 AM EDT Saturday
Area Forecast Discussion...Updated
National Weather Service Billings MT
858 PM MDT Thu Aug 31 2017
An area of thunderstorms continues to push southeast out of
southeast Montana and into South Dakota. Winds still look to
increase tomorrow morning behind a tonight`s shortwave. Winds at
700mb with the 00z run of the NAM are still approaching 30 kts and
with mixing during the day tomorrow could mix to the surface. The
current forecast still looks on track. Reimer
.SHORT TERM...valid for Fri and Sat...
HRRR model continues to indicate increased smoke moving in from
the west behind a departing front this evening and hanging around
through the day tomorrow. Today, we have already seen some
unhealthy levels of smoke in eastern Montana due to several large
fires in Powder River and Custer counties. Isolated to scattered
showers and thunderstorms possible as an upper-level shortwave
moves through southeastern Montana this evening. Increased
northwest winds over the eastern Plains tomorrow has prompted the
issuance of a Fire Weather Watch tomorrow afternoon and evening.
Expecting humidity levels near 20 percent with gusts up to 30 mph
during the afternoon in the Plains. Further west it will be dry
and warm again with no appreciable chance of rain and winds look
to be lighter than out east. Ridging moves in from the west on
Saturday which will bump temperatures into the low to mid 90s,
decrease winds, and keep the skies cloud free. Walsh
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
High pressure ridging will continue one more day Sunday. A strong
cold front sweeps across the forecast area late Sunday which will
shift the ridge and axis westward over the Pacific Northwest
Monday and Tuesday. It is still a bit far out in time on the exact
arrival of the front but right now it looks to arrive during the
afternoon hours Sunday. Pre-frontal mixing ahead of the front will
allow for temperatures be hot ahead of the front on Sunday with
temperatures approaching or exceeding records for some locations.
Temperatures will be much cooler on Monday and Tuesday, but these
readings will actually be about normal for this time of year.
Ridging begins to build once again by the middle to end of next
week allowing for temperatures to return to above normal readings.
Aside from mid and low level smoke moving into the region after
04z skies will be mostly clear through the night. VFR conditions
will prevail but some reductions in visibility to MVFR levels due
to smoke is possible through 15z. Did not warrant inserting into
the TAFs due to low confidence. Northwest winds will increase
across the region tonight from 05z to 15z as a front works its
way through the region. Dobbs
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
BIL 061/088 058/093 060/099 059/079 053/080 052/084 055/087
10/K 00/U 00/U 00/U 00/U 00/U 00/U
LVM 051/087 050/094 051/098 051/084 044/082 044/086 047/087
10/K 00/U 00/U 00/U 00/U 00/U 00/U
HDN 057/088 054/095 057/097 055/082 049/082 048/086 051/089
00/K 00/U 00/U 00/U 00/U 00/U 00/U
MLS 063/088 058/094 060/100 057/077 049/079 048/084 052/087
20/K 00/U 00/U 00/U 00/U 00/U 00/U
4BQ 061/087 055/094 059/099 055/078 049/078 048/083 051/087
30/K 00/U 00/U 00/U 00/U 00/U 00/U
BHK 059/086 055/092 055/095 053/075 045/075 045/080 048/084
30/K 00/U 00/U 00/U 00/U 00/U 00/U
SHR 055/085 052/093 054/099 053/080 046/078 044/082 047/086
20/K 00/U 00/U 00/U 00/U 00/U 00/U
MT...Red Flag Warning in effect until 9 PM MDT Friday FOR ZONE
Fire Weather Watch in effect from Friday afternoon through
Friday evening FOR ZONES 131>133.
WY...Fire Weather Watch in effect from Friday afternoon through
Friday evening FOR ZONE 274.
Area Forecast Discussion
National Weather Service Charleston SC
945 PM EDT Thu Aug 31 2017
A warm front will lift north of the region through Friday
morning as Tropical Depression Harvey moves across the lower
Mississippi Valley. A cold front will approach from the north
this weekend. High pressure will then prevail early next week
before another front approaches the region during the second
half of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 925 PM: Stratiform rainfall was slowly dissipating over
the SC Lowcountry, a few new clusters of showers were developing
across inland SE GA. The new shower activity appears to be
associated with the second round of rainfall, forced by LLVL
isentropic lift. I will update the forecast to adjust PoPs, sky,
As of 720 PM: Overall, convection has trended weaker across SC
over the past half hour, with a few stronger cells along the SE
GA coast. The GA activity should push over the coastal waters
over the next one to two hours. SC activity should gradually
fade. I will update the forecast to update POPs and WX.
Previous discussion: Updated POP and Wx grids to account for
observed trends with ongoing convection. HRRR and 12Z NSSL-WRF
have generally prognosed the behavior and timing of this
convection reasonably well, if not a little slower than reality
as is typical. Based on trends, the convection should be
weakening as it moves offshore of most zones by 01-02Z. Still
cannot completely rule out an isolated tornado closer to the
warm front and highest low-level helicity. After this line
pushes offshore, mostly dry conditions are expected overnight.
Increasing low-level jetting will keep temperatures warmer than
last night, mainly mid to upper 70s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday and Saturday: Southerly flow between the remnants of Harvey
inland and Atlantic high pressure will continue to advect deep
moisture into the region as a cold front extending from a low
pressure system north of Maine sinks south into North Carolina. This
pattern supports a chance of showers beginning early Friday,
increasing to numerous showers and thunderstorms through the
afternoon and evening. Sufficient surface-based CAPE and shear will
support some strong to marginally-severe thunderstorms, with
greatest potential in northern zones due to closer proximity to the
front. Despite continual degradation of Harvey`s remnants, residual
lower surface pressure and heights aloft will make it easy for a
parent low pressure system in Canada to induce secondary, downstream
low pressure formation over the mid-Atlantic states. Guidance
suggests this low pressure will slide offshore into the mid-Atlantic
coastal waters by Sunday evening as it races northeast. Divergence
overhead under the right-entrance region of a passing upper
level jet will contribute to the formation of numerous showers
and thunderstorms over much of the area Friday night into
Saturday, until the bulk of deep-layered moisture shifts
offshore Saturday evening. Temperatures through the period will
be within 1-2 degrees of normal.
Sunday: A relatively drier atmospheric column is expected to fill in
behind the low pressure as it departs the mid-Atlantic region. While
the majority of precipitation will remain offshore, a few showers or
isolated thunderstorms near the coast during the afternoon cannot be
ruled out. Near-normal temperatures are anticipated.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Dry high pressure will build from the west early next week behind a
low pressure system shifting off the Mid-Atlantic and Northeast
coasts. However, a few showers and/or thunderstorms will be possible
near coastal locations Monday, followed by slightly greater precip
coverage on Tuesday as mid/upper lvl energy shifts along the western
edge of a mid/upper lvl ridge axis over Florida. High pressure
should prevail into mid week ahead of a large mid/upper lvl trough
of low pressure expanding over the Central United States. A cold
front associated with this feature should then sweep across much of
the Eastern Conus during the middle of next week. Given the setup, a
southerly flow ahead of the front should support increasing chances
of showers and/or thunderstorms through Wednesday. High temps will
be dependent on cloudy skies and precip coverage, but should peak in
the upper 80s to around 90 degrees, warmest in Southeast Georgia.
Overnight lows should range in the upper 60s/lower 70s Sunday night,
then lower to middle 70s into the middle of next week.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Thunderstorms east of KSAV at the onset of the KSAV 0z TAF
should push east over the coastal waters. It is possible that
lightning and thunder will be observed through 2z. Light rain
should pass over KCHS through 2z, little to no impact on
conditions. I expect that considerable debris clouds will remain
over the terminals through most of tonight. Deep convection will
be possible across the terminals again tomorrow by 20-21Z.
Extended Aviation Outlook: Probabilities for periods of restrictions
at either terminal due to direct impacts from showers/thunderstorms
will generally increase each day into the weekend. Prevailing VFR
conditions are expected early next week.
Tonight: Southerly winds to increase as a warm front passes
north through the waters and a stronger low-level jet sets up.
Speeds will increase to 15-20 kt for the Georgia waters with 15
kt across the South Carolina waters. Seas will increase as a
result, reaching 2-4 ft nearshore waters with a solid 4 ft over
the offshore waters. There could be a few gusts to 25 kt after
midnight, mainly near the Gulf Stream, but do not anticipate
the durations to be frequent enough to justify a Small Craft
Friday through Monday: The coastal waters will generally remain
under the influence of Atlantic high pressure, with conditions
expected to remain below Small Craft Advisory levels this weekend
and early next week. In general, south winds will periodically veer
southwest while peaking 15-20 knots early this weekend, before
turning offshore and gradually diminishing to around 10 kts or less
early next week. Seas will range 2-4 feet.
Area Forecast Discussion
National Weather Service Dodge City KS
530 PM CDT Thu Aug 31 2017
...Updated aviation section...
.SHORT TERM...(This evening through Friday)
Issued at 227 PM CDT Thu Aug 31 2017
Some scattered thunderstorms will be possible early tonight near
a surface boundary that will be located over eastern Colorado
however these storms are expected to weaken as they move
east/southeast. A few of the models do suggest that some light
showers will spread into portions of far west central Kansas
between midnight and 6 am. At this time am not overly excited
about precipitation chances based on the NAM and RAP forecast
soundings near the Colorado border between 06z and 12z Friday but
still will favor a slight chance for something early this morning
west/northwest of a Garden City should a few of these storms hold
There will also be some mid to high level clouds spreading east
from these storms during the overnight hours and given this
increase in cloud cover do not anticipate that lows tonight will
be as cool as the last few night. The previous forecast with lows
around 60 still look on track for most of western Kansas.
An upper level trough, located over the Pacific Northwest at 12z
Thursday, will cross the Central Rockies during the day on Friday
as the eastern Colorado surface boundary approaches the
Colorado/Kansas border. Ahead of this surface boundary the
southerly winds will increase into the 15 to 20 mph range as some
mid and high level moisture spreads into western Kansas. The
mixing depth Friday afternoon based on model soundings is forecast
to be around the 850mb level and based on this the highs on
Friday are expected to range from 85 to near 90.
.LONG TERM...(Friday night through Thursday)
Issued at 227 PM CDT Thu Aug 31 2017
An upper level trough will cross the western Kansas early Friday
night. Based on the latest models earlier this afternoon it
appears that the better moisture and lift ahead of this wave will
be located across northern Kansas as this upper wave passes. Also
the better instability early Friday evening will be focused near a
surface boundary located from southeast Colorado into northwest
Kansas. The storms that do develop along this boundary late Friday
may briefly strengthen but as they move east/southeast they are
expected to weaken as they cross western Kansas during the
overnight hours. Early in this event as some of these storms
strengthen a few of the stronger storms may be capable of
producing hail up to quarters and some gusty winds.
Once this upper trough passes a period of dry weather will return
as temperatures warm into the 90s over the Labor Day weekend. The
main question this weekend into early next week is how warm
temperatures will climb ahead of a cold front that will be
approaching southwest Kansas through Monday. All models agree with
that the warmer air will be located just ahead of this surface
cold front based on the 850mb thermal ridge axis, however where
this front will be Sunday and Monday afternoon is unclear. The
ECMWF is the most aggressive with this frontal boundary pushing
the front into southern Kansas by late day on Monday. The GFS at
00z Tuesday has this surface boundary in northern Kansas. Given
these differing solutions the temperatures on Monday will be
a little tricky. On Sunday it still appears that guidance is too
cool with the highs based on the 850mb temperature trends. Some
highs in the upper 90s is not completely out of the question in
west central or north central Kansas Sunday afternoon. Highs in
the mid 90s likely further south. On Monday the highs again are
will climb into the mid to upper 90s despite the uncertainty on
the frontal boundary late day. This is based on the forecast 2M
temps from the ECMWF and what the EKDMOS suggests for Highs on
Monday. The only question is where the warmest temperatures will
There will also be a chance for overnight convection along and
behind this surface boundary as a northern branch upper level
trough approaches the Central Plains. Models today remain in good
agreement with the better opportunity for convection across
central Kansas being on Tuesday as the northern upper wave
As the precipitation ends and the cold front drops south into the
Oklahoma on Tuesday some colder air will return to western
Kansas. It currently appears that some fall like temperatures
will briefly return mid week as a cool dome of high pressure
builds across the Central Plains. For Tuesday will need to monitor
the cloud cover and if we do not see any sun during the afternoon
then highs Tuesday afternoon may struggle to get much warmer than
the lower 70s. Wednesday will be warmer but still unseasonably
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 529 PM CDT Thu Aug 31 2017
VFR conditions will prevail overnight with mostly clear skies.
Winds will be light and from the southeast.
.PRELIMINARY POINT TEMPS/POPS...
DDC 58 86 61 91 / 0 10 40 10
GCK 58 87 60 91 / 10 10 30 0
EHA 59 88 62 89 / 0 10 30 0
LBL 61 89 62 90 / 0 10 30 0
HYS 60 85 61 90 / 0 10 40 0
P28 60 87 64 89 / 0 0 50 10
Area Forecast Discussion
National Weather Service Des Moines IA
707 PM CDT Thu Aug 31 2017
.SHORT TERM.../Tonight through Friday/
Issued at 200 PM CDT Thu Aug 31 2017
Stubborn stratus has been the main forecast challenge on the
short term side today. The band of lower ceilings resides in the
vicinity of a shallow backdoor front that is slowly sagging
southwest. High-res models suggest the potential for a few
showers and storms late this afternoon and early evening near the
frontal axis in central Iowa. Latest RAP analysis indicates
1000-1500 J/kg of MLCAPE and weak theta-e convergence in the
925-850mb layer, but the spatial coverage of any convective
activity will be sparse at best as favorable upper level
kinematic support remains well west of the forecast area.
Areas of fog are possible again early Friday morning, mainly from
north central through southeast Iowa. NAM/GLAMP favor fog, while
the HRRR-TL/SREF/RAP camps remain clear. Upwind obs show a
slightly cooler and drier air mass filtering behind the front,
which may be enough to limit the fog potential tonight. Any
mention of fog has been left out of the grids for now due to low
.LONG TERM.../Friday night through Thursday/
Issued at 200 PM CDT Thu Aug 31 2017
Primary focus of the long term period is temperatures with a warm
up expected through the weekend followed by a strong cold frontal
passage early next week. Weak ridging aloft will lead to quiet
conditions through the weekend. Low level southerly flow ramps up
by Sunday as an upper level trough digs southeast into the
northern Rockies. Strong warm air advection pushes 850mb temps
above 20C for Sunday and Monday with afternoon highs in the mid to
upper 80s. Would not be surprised to see some places in southern
Iowa break into the 90s. Euro and GFS have come into much better
temporal agreement with the upper level low as it digs south and
becomes highly amplified. This will shove a strong cold front
through the area Monday night. Isolated to scattered storms are
possible with the frontal passage, but the extent and strength of
the activity will be limited by dry air and weak instability.
Expecting highs to drop back into the 60s and 70s for the middle
of the week. Overnight lows were adjusted a few degrees lower from
the inherited Superblend to better match the lows favored by
ECE/MEX guidance. This would be an early taste of fall as the Des
Moines metro has not seen temperatures in the 40s since May.
.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 707 PM CDT Thu Aug 31 2017
Stratus continues to linger across north central Iowa this evening
but should slowly diminish with drier air pushing in from the
northeast. Otherwise, some light fog will remain a possibility
overnight through sunrise. Widespread VFR conditions are expected
into Friday with good weather for general aviation.
Area Forecast Discussion
National Weather Service Indianapolis IN
1121 PM EDT Thu Aug 31 2017
The Aviation section has been updated below.
Issued at 224 PM EDT Thu Aug 31 2017
Low pressure and associated remnants from Harvey across northwest
Mississippi will push northeast toward the Ohio Valley tonight.
This will result in dry weather tonight for central
Indiana...however showers are expected to arrive mainly across the
southern parts of the Indiana on Friday and Friday Night.
Harvey leftovers are expected to slowly exit the area on
Saturday...and rain will end from southwest to east central parts
of Indiana. Much of the north half of the state should remain dry.
Dry weather is then expected to return for the end of the holiday
weekend as High pressure builds across the middle Mississippi and
Ohio river valleys.
The passage of a cold front on Tuesday will usher in a blast of
cooler fall-like air for the second half of next week.
.NEAR TERM /Tonight/...
Issued at 1000 PM EDT Thu Aug 31 2017
Lowered min temps a bit based on latest near term guidance and
wetbulb temp progs across the south where precip may arrive before
daybreak. Additionally, increased wind speeds and gusts tonight
into tomorrow per upstream obs and HRRR and BUFKIT guidance.
Previous discussion follows.
Issued at 224 PM EDT Thu Aug 31 2017
Surface analysis early this afternoon shows low pressure over
Mississippi and High pressure was in place across the northern
Great Lakes. GOES16 shows bands of clouds associated with Harvey
remnants streaming across Central Indiana. A NE surface flow was
in place with dew points in the upper 50s. National Radar Mosaics
show precipitation contained relatively close to the center of
circulation...over Arkansas and Mississippi.
GFS and NAM suggest that the low will push in to the Tennessee
River Valley late tonight...spreading rains across
Tennessee...Kentucky and far southern Indiana. Forecast soundings
and Time heights remain dry for tonight as best moisture has yet
to arrive...and dry NE surface flow remains in place. We will
expect increasing clouds tonight as the cloud shield with the low
continues to thicken upon approach. As for temps...with with a
tropical air mass arriving along with cloud cover...will trend
lows at or above than the forecast builder blend.
.SHORT TERM /Friday through Sunday/...
Issued at 224 PM EDT Thu Aug 31 2017
GFS and NAm both push the surface low farther northeast on Friday
and Friday Night...spreading cyclonic circulation across Indiana
and spreading moisture into the southeast half of the state. Time
Heights and forecast soundings show deep moisture and strong lift
arriving mainly south of Winchester-Vincennes line by Friday
afternoon and Friday night. Strong pressure gradient across the
area will also result in gusty winds on Friday afternoon and
Friday Night. Given the favorable forcing will trend pops highs
across the far SE...trending lower farther northeast. At this time
locations like Lafayette and Kokomo may stay dry due to the
expected path of moisture. Given the expected clouds and
rain...will trend highs on Friday at or below the forecast builder
blend. Will trend Friday Night lows at or above the blend.
Models suggest that by Saturday the Center of circulation will
have move to west Central Ohio. Time heights and forecast
soundings show moisture across the eastern Half of the state
during the morning hours...however dry air and subsidence begins
to build across the western half of the state...denoting clearing.
As Harvey leftovers get farther north...acceleration should
increase also...ending precipitation quickly on Saturday afternoon
from West to East. By 00Z Sunday...ridging and subsidence is
quickly building across Indiana denoting dry weather. Thus will
end pops on Saturday morning and trend them lower as the day
Dry weather looks to remain in place on Sunday as GFS and NAm
suggests surface high pressure in place as forecast soundings
show a dry column with subsidence and a mid level inversion. Thus
Partly cloudy/mostly clear and temps below seasonal normals given
the expected NW flow in the wake of the departed low.
.LONG TERM /Sunday night through Thursday/...
Issued at 233 PM EDT Thu Aug 31 2017
Dry weather will be in place to start the long term with broad
high pressure sliding off to the southeast and warm southerly
component flow into the area. By Monday afternoon and evening a
cold front will approach from the northwest and bring chances for
showers and isolated thunderstorms with it. The best chances with
this front appear to be overnight Monday as the front moves
through. Chances will continue through Tuesday as the upper trough
axis moves through the area, but after that conditions should be
dry and cool with another Canadian high pressure system building
in over the area. Given some model differences in timing of the
frontal system and upper trough passage, confidence is moderate.
.AVIATION /Discussion for the 01/06Z TAFs/...
Issued at 1122 PM EDT Thu Aug 31 2017
VFR through the period, with the exception of some MVFR ceilings
late in the period at BMG.
Harvey remnants will move into the region during the period, and
the predominant impacts will be some shower activity at IND and
especially BMG, and gusty northeast winds across the area.
Cannot rule out a rumble of thunder but this is far too low
probability for inclusion.
Winds be in the mid teens with gusts into the low to mid 20KT
range generally out of the northeast much of the period.
Area Forecast Discussion
National Weather Service Elko NV
318 PM PDT Thu Aug 31 2017
.SYNOPSIS...Isolated to scattered thunderstorms will end later
this evening. A strong ridge of high pressure will build in from
the west beginning tonight and will bring much above normal
temperatures to the area for Labor Day weekend and into next
week. Sky conditions should be mainly clear Friday through
.SHORT TERM...Tonight through Saturday
Isolated to scattered pulse type thunderstorms are ongoing this
afternoon in all but Humboldt county, where drier air has already
moved in, but should quickly dissipate later this evening as a
dry airmass continues to move into Nevada from the northwest.
This will bring mainly clear skies the next couple of days for the
start of the Labor Day weekend, with temperatures warming back
well into the 90`s most valleys by Saturday. Winds will be on the
lighter side under the building ridge of high pressure.
The HRRR model continues the transport of smoke into our area and
so continued areas of smoke through the night.
.LONG TERM...Saturday night through next Thursday.
Models agree on general pattern with strong upper ridge over the
Great Basin through the period and Tropical Storm Lydia now over
Cabo San Lucas heading up along Baja and then turning left into
the Pacific. But.....
The GFS and Euro differ completely on where the strung out
moisture will go as it weakens. The Euro has it moving out to sea
with the dying system. The GFS has a large slug of it moving up
along the Sierra Nevada line and some slopping over into central
Have leaned toward a mix of the two, but probably a little heavy
on the GFS. Pops increase into the extended over the entire
forecast area but are still not impressive for QPF...in the 20s at
Temps will still be warm under the governing ridge, and so dry
storms will cover central, eastern, and northern Nevada but in an
It is, after all, still summer.
.AVIATION...Thunderstorms becoming more common Thursday afternoon
but still isolated. Some of the storms are on the strong side with
small hail and gusty winds occurring. Best chance for VCTS around
KEKO and KELY. Other storms en route from northeast of KTPH to
KELY. Most storms are east of a line from around Owyhee to Austin
to Round Mountain and moving slowly east. Ceilings and visibility
will be VFR. Erratic cross winds could occur near runways. Smoke
from fires in western Nevada covering large areas of the state.
Not reducing surface visibility but may reduce slant visibility
and possible obscure an occasional mountain peak. It`s hotter than
normal, so density altitudes will be higher than normal.
.FIRE WEATHER...Isolated thunderstorms are ongoing this
afternoon in Fire Weather Zones 469 and 470 which are on the
drier side while thunderstorms in central Nevada fire zones are
more scattered and on the wetter side with some heavier showers
being reported as well as some small hail. Erratic wind gusts can
still occur with any storm. All storms will taper off later this
evening. Drier air moves into the region tonight through Saturday,
lowering RH and bringing temperatures much above normal once
again. Winds are expected to remain under critical conditions as
high pressure builds in.
Area Forecast Discussion
National Weather Service Blacksburg VA
1146 PM EDT Thu Aug 31 2017
The remnants of Harvey will move into the Tennessee Valley
Friday and into the Ohio valley Saturday as high pressure over
the Great Lakes surges down east of the Appalachians. This will
allow rain to develop across the region late tonight and
continue through tomorrow. Showers will continue Saturday as
Harvey moves northwest of the area, then end Saturday evening.
High pressure will build into the region for Sunday and continue
into the first part of next week.
.NEAR TERM /THROUGH FRIDAY/...
As of 1140 PM EDT Thursday...
Adjust temperatures, dewpoints and pops some to reflect latest
trends and observations. Temperatures are cooling more in the
west than the east. A blend of the HRRR, GLAMP25, and existing
forecast yielded very reasonable values. Dewpoints needed less
adjustment, but were too low in the southeast part of the CWA
where dewpoints have come up to near 70F. Otherwise, adjusted
pops down for the next few hours as radar trends showing
precipitation well back to the southwest yet at this hour.
Followed HRRR for overnight trends with pops ramping up toward
categorical after 08Z.
As of 745 PM EDT Thursday...
No need for any significant changes at this time. One heavy
shower moved through the Danville area this evening, otherwise
only sprinkles or light showers dotting a few areas. Following
latest HRRR, would not expect much precipitation until after
midnight, spreading north from the southwest with time after
As of 300 PM EDT Thursday...
Late afternoon radar shows showers mainly along and south of
route 460 ahead of a cold front sagging southward across the
region. The showers will push off to the south this evening
before the remnant circulation of Harvey moves up the
Mississippi valley and combines with high pressure over the
Great Lakes forming a strong wedge east of the Appalachians to
buckle the front and create strong isentropic lift over the
region. This will allow rain to surge back into the area from
the south late tonight, then continue through Friday.
Differences in timing and placement of features among guidance
members are making things difficult, but still expect the
heaviest rain to fall across the VA/NC piedmont and Southside
VA, with some local enhancement due to orographic effects along
the Blue Ridge, where amounts of 1.5 to near 2.0 inches are
expected with lesser amounts further north and west of the Blue
Ridge. Ensemble hydro models indicate the current low flow along
area waterways will be able to absorb runoff without causing
widespread hydro issues. However, the situation will continue to
be monitored closely to see if locally higher amounts and/or
training cells develop and cause local problems.
Shear profiles along and south of the wedge boundary tomorrow
continue to be robust with large looping hodographs. The
limiting factor for severe weather will be how much instability
can develop, and given the amount of shear expected it will not
take large values of CAPE to support severe storms. The key will
be how much instability can pool ahead of the boundary before it
pushes far enough south and the cool stable wedge shuts down the
threat. Believe the best chance for cells capable of tapping
into the shear to develop will be far southwest from the
Mountain Empire of VA to the mountains/foothills of NC where
the wedge normally has difficulty penetrating, and extending
further south into the NC piedmont. The situation will be
monitored quite closely tomorrow.
Temperatures tonight will be in the low to mid 60s east of the
Blue Ridge, with readings around 60 to the west. Friday will be
quite cool as the wedge builds down tomorrow with temperatures
in the north likely falling throughout the day, and any heating
in the south eventually shut off by the surging wedge.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 325 PM EDT Thursday...
Low pressure/Harvey will be in south-central KY Friday evening while
a front situates itself east of this low into far SW VA, then
southeast into central NC with high pressure wedging southward from
The upper pattern favors a slow moving system, so inclined to keep
categorical to likely pops in Friday night, then should see a dry
slot work in from the NC foothills/piedmont Saturday, though with
upper low still west and southwest flow aloft, plus moisture should
still see a scattered coverage Saturday with higher chance in the
mountains. Heading through Saturday night, the Harvey remnant moves
into the mid-Atlantic, while the upper low opens to a trough and
weakens. Low level flow turns west to northwest and could see
residual showers in the mountains Sunday.
Temps stay well below normal for highs Saturday, the slide back
closer to normal Sunday as sunshine starts to return.
Heaviest rainfall looks to occur Friday evening with best upslope
and overrunning the wedge, where all 3 models showing two distinct
areas of heavy rain, one across KY into northern WV and the other
over the NC piedmont into southern VA. A shadow of sorts, where rain
will be less is showing up in most models from the mountain empire
of SW VA into the Alleghanys.
Will have to watch for training of deeper convection over the
piedmont especially into Friday evening for localized flood
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 325 PM EDT Thursday...
Models are in agreement into developing a digging trough from the
Great Lakes into the TN Valley through midweek, but some differences
beyond Wednesday as too how far east the trough axis moves, in
relation to strength/position of upper ridge over the western
Needless to say should be fair and seasonably warm Monday. Frontal
boundary will be pushing into the mountains by Tuesday evening with
increasing chance of showers/some thunderstorms along/ahead of it.
Ahead of it should be warm/humid Tuesday. Frontal boundary slows
down per ridge offshore with waves of low pressure setting up along
it. This should keep a good threat of showers around for our area
Wed-Thu. Temps should fall back to or below normal, with highs more
than likely cooler than normal ranging from mid 60s to lower 70s
west, to mid to upper 70s east.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
As of 750 PM EDT Thursday...
Poor aviation conditions expected through most of the TAF valid
period. We will start with a period of mostly VFR ceilings, but
that will quickly deteriorate after 06Z. Three synoptic
situations that will drive the weather through the period.
First, low pressure developing along the SC/NC coast and helping
to pull a feeder band essentially associated with the remnants
of Harvey, now across northern LA, from the AL/GA area toward
the coast. Some of this moisture will work into the Piedmont
late tonight/Friday morning before shifting eastward toward the
The next factor of importance is the development of a wedge as
high pressure moves toward New England. The rain and coastal low
pressure will help reinforce the wedge as well.
Finally, the remnants of Harvey will be moving northeast through
central and northeast KY Fri and Sat. The heaviest rainfall
associated with this will remain to our northwest, but this will
keep the weather unsettled with potential for a few feeder bands
to affect the area, especially Saturday.
Ceilings are expected to fall into the MVFR and even the IFR
range as rain moves into the region late tonight/early Friday.
Little to no improvement is expected during the day Friday.
Visibilities will remain VFR through the evening, then fall
mostly in the MVFR range late tonight and remain there through
the day Friday. Some IFR visibilities can be expected in the
higher terrain where the ceilings fall below 010.
Winds will be mostly light and variable or southwest 3-5kts this
evening, becoming northeast to east late tonight into Friday
morning as the wedge develops and intensifies across the region.
With the coastal low/front developing and high pressure
strengthening across the northeast U.S., expect winds to become
stronger and gusty. Sustained speeds of 10-12kts with gusts of
20-22kts are definitely not out of the question, especially at
LYH, DAN, and BLF. Will definitely need to watch the winds at
BLF as with this type of pattern, they could become quite strong
and gusty in that region. The HRRR depicts quite strong/gusty
winds by Fri afternoon across much of the region.
Finally, isolated thunderstorms will be possible Friday
afternoon across the Piedmont, mainly of NC. Will only include
in the DAN TAF at this time.
Medium to high confidence in ceilings through the TAF valid
Medium to high confidence in visibilities through the TAF valid
High confidence in wind speed and direction through the TAF
Low confidence in thunderstorm potential Friday afternoon.
Extended Aviation Discussion...
The remnants of Hurricane Harvey will track northeast through KY
and into eastern OH/western PA Saturday, then become absorbed in
the general synoptic pattern moving toward the northern Mid-
Atlantic Sun-Mon. Harvey will no longer be a factor in our
weather after Saturday, and its main effects will remain
northwest of our region. Widespread precipitation will decrease
Saturday as the remnants of Harvey moves to our northwest and
the coastal front shifts well southeast of the area. Some VFR
ceilings may be possible Saturday, but expecting mostly MVFR
conditions. Sunday into early next week will see improving
conditions to mostly VFR as high pressure moves southeast into
the region as Harvey exits to the northeast. The exception will
be late night/early morning patchy dense fog at the usual
locations, e.g., LWB and BCB.