Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Bismarck ND
1002 am CDT Tuesday Jun 30 2015
issued at 1002 am CDT Tuesday Jun 30 2015
Smoke from Canadian fires has begun to diminish in intensity the
past hour or so...with visibility in Williston rising from 1-2 miles
to 4 miles...though Crosby is still reporting 1 mile visibility.
Will revisit this issue around noon to see whether mixing with winds
and potential rain showers helps mix out the smoke at the surface.
Band of light rain showers has shifted into central North
Dakota...with the southwest free of rain showers. Have updated
precipitation chances to reflect this for the morning hours. Later this
afternoon we are still expecting convection to develop in the west
by mid-afternoon...with some strong to severe storms possible.
Current forecast on track.
issued at 623 am CDT Tuesday Jun 30 2015
Forecast on track with this issuance. Two bands of showers
currently...one moving east across far northwest ND...the other
across central North Dakota along a surface boundary. Some weak
instability although zero lightning strikes the past few hours.
Will keep a slight chance/isolated thunder mention through the am
Short term...(today and tonight)
Issued at 332 am CDT Tuesday Jun 30 2015
Forecast highlights include severe thunderstorms west this
afternoon into Tuesday night...smoke from Canadian wildfires
reducing visibilities to between one and three miles across
northwest North Dakota. Will continue the Special Weather
Statement for the smoky conditions northwest through the morning
and let the dayshift re-evaluate later in the morning.
Early this morning...a backdoor cold front that past through The
Turtle mountains and James River Valley Monday...is now located
roughly from Bowbells...to Stanley...south to Glen Ullin and into
Mobridge South Dakota. Water vapor showed a shortwave over north
central North Dakota...riding over this front resulting in
showers/thunderstorms to develop over Morton/Grant/Sioux/Emmons
counties...and into central South Dakota. Should see diminishing
activity as the shortwave continues to move southeast. Regional
radar shows reflectivitys increasing over southern Saskatchewan
and eastern Montana..associated with another leading shortwave. As
this slides across western and south central North Dakota this
morning...expecting renewed showers and thunderstorms to develop.
Will see some breaks in the areal coverage today...but timing how
long and which areas will be difficult. Have pretty much trended
with scattered showers and thunderstorms through the morning then
increased to likely in the afternoon through the evening.
The main concern will be this afternoon and evening as a potent
shortwave trough currently working into southeast Alberta...shifts
into northeast/eastern Montana between 18z-00z. Surface low
pressure and a formidable frontal system develop in response
across southeast Alberta...into southeast Montana and western
South Dakota. Remnants of this mornings backdoor cold front
mentioned above may provide additional low level convergence this
afternoon/evening as it weakens and shifts further west. Storm Prediction Center has
now increased the severe thunderstorm risk category to a slight
chance west...and expanded the marginal area to near central
North Dakota. Main threats will be large hail/damaging winds/and
closer to the front/greatest shear will be the possibility for a
couple of tornados. Cape values per GFS increase to around
1000-1300 j/kg west with impressive 0-6km bulk shear of 55-60kt.
The European model (ecmwf) advertises cape of around 1800 j/kg with 0-6km bulkshear
of 50-55kt. Have injected severe mention in the gridded data/point
and click...and will carry this message out into the state forecast/severe weather potential statement
Long term...(wednesday through monday)
Issued at 332 am CDT Tuesday Jun 30 2015
Northwest flow aloft remains in place Wednesday through Friday night
across the northern plains. Through Thursday...several embedded
waves will push southeast across the region...with a quasi-
stationary/redeveloping surface boundary bringing decent chances for
showers and thunderstorms area wide. Kept wording at chance until we
get closer to specific periods when probability of precipitation should be able to be better
fine-tuned. A few stronger storms once again possible Wednesday
daytime across the west near a stationary surface trough where highest
instability will be collocated with robust bulk shear.
Will go with a dry Friday/Friday night period when models move the
aforementioned boundary off to our south and east with southerly
return flow over the Dakotas.
Deep area of low pressure moving slowly east across southern Canada
will dominate the weather across the northern plains this weekend
and into next week. As the upper low crosses the Alberta rockies
Saturday...our flow aloft transitions to zonal with low/middle level
flow south/southwesterly increasing ahead of a strong frontal
boundary developing ahead of the upper low off to our north and
west. This will promote strong warm air advection with highs Saturday warming back
into the low 80s to low 90s after highs Wednesday & Thursday 70-80. As the
upper low moves east across Saskatchewan and Manitoba Sat night -
Sunday night...strong cold front will push southeast across North
Dakota and will be the focus for widespread showers and
thunderstorms. A few stronger storms will be possible Saturday
night/early Sunday when models show the best instability and shear
coupled together. Saturday afternoon more uncertain with a cap
likely in place ahead of the cold frontal boundary.
Secondary/backdoor cold front Monday/Monday night will see highs in
the 70s for Sunday. Would not rule out 60s across the east depending
on how strong the cold air advection is depicted for Monday over the next few model
runs. We warm back up middle-week when an upper level ridge out west
builds east across The Rockies.
Aviation...(for the 06z tafs through 06z Tuesday night)
Issued at 623 am CDT Tuesday Jun 30 2015
Smoke will continue to reduce visibilities at kisn to around 2sm/MVFR
through 18z...possibly longer. Rain showers should help temporary
improve visibilities. Isolated to scattered showers at all terminals except
kjms through 18z...then becoming more widespread during the late
afternoon into Tuesday night. Severe thunderstorms possible from kisn
south to kdik. Have kept ceilings VFR although MVFR ceilings are possible
after 00z. Confidence not high enough at this time for a predominate
long term...New Hampshire