Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
1249 PM CDT Thursday Jul 24 2014
issued at 1245 PM CDT Thursday Jul 24 2014
Necessary to expand probability of precipitation into west central Minnesota for another hour or
two as precipitation band has held together. Stronger elevated convection
poised to exit our far southern forecast area leaving mainly rain showers into early
afternoon. Also monitoring wind speeds on back edge of precipitation band.
Good drying of echoes and pressure falls via msas indicating
potential wake low development. Currently expecting possible 25 to
40kts with this feature. Temperatures well below expected values
across the far west but solar should allow for quick recovery.
Update issued at 939 am CDT Thursday Jul 24 2014
Convection across the far western forecast area beginning to outrun favored
instability/cape. Strongest cells on southern flank propagating
south-southeast feeding into nose of low level jet. Increased probability of precipitation across the
far west through the remainder of the morning but still anticipate
weakening as cells push east. No other changes.
Update issued at 643 am CDT Thursday Jul 24 2014
There is an intimidating line of thunderstorms marching across
North Dakota this morning. Model guidance is no help as to how
this line will evolve over time...and will need to use experience.
Instability axis remains across the western Dakotas...and
transitions to a stable airmass across eastern North Dakota.
Thus...anticipate that this line of storms will begin to weaken
in the next hour or two...and although remnants will make it into
this forecast area...it will be much weaker. The current 20-30 probability of precipitation for later
this morning should still get this point across. The main idea
that the best chance for thunderstorms will be after sunset still
seems the most reasonable.
Short term...(today through friday)
issued at 345 am CDT Thursday Jul 24 2014
A stable airmass remains across the forecast area...with moderate to strong
instability located across the western Dakotas. Not much change
expected through the day. There is a stronger shortwave that will
ride over the upper ridge and into the forecast area later this morning. Any
associated activity will be moving into a stable airmass...with
dissipating convection possible across eastern North Dakota. Will
cover this precipitation chance with 20-30 probability of precipitation (following mainly the
hrrr guidance)...and will add more detail with the 7am update.
Otherwise...much of the day and evening will be dry. The best
chance for thunderstorms will be overnight (likely after midnight)
as convection from the west (initiated by a cold front/surface trough)
moves into the region. Models indicate the moderate instability
will move into eastern North Dakota...along with deep layer shear
around 40 knots. These parameters would favor supercell storms.
However...a strong 850mb low level jet will be focused near our
southern forecast area at 06z...then veer southeast into southern Minnesota by
12z. Thus...not sure if there will be enough dynamics to support
nocturnal severe storms. Neighborhood probability type products
show very low chances for severe storms past sunset. Although
scattered thunderstorms are likely...the stronger storms will be
Guidance is now quicker with the passage of the cold front/surface
trough on Friday...meaning that the afternoon/evening severe
threat is likely shifted east of the forecast area (into north central
Long term...(friday night through wednesday)
issued at 345 am CDT Thursday Jul 24 2014
Friday night-Saturday night...upper level low will propagate from
Saskatchewan into northern Minnesota. Showers and possibly some
thunder will be possible across the northern portions of the forecast area.
Sunday-Wednesday...the strong upper shortwave trough will rotate
southeastward into the Great Lakes on Sunday. Energy diving south
on the back-side of the upper low and cool air aloft could still
result in a bit of shower/storm activity. Cool highs in the upper
60s to low 70s are expected with 850 mb temperatures in the 7-10c range.
Otherwise...through the rest of the period...a return to an
amplified East Coast upper trough/western US ridge is
expected...with surface high pressure slowly working eastward across
the plains. A slow moderation in temperatures to near seasonable averages
will occur. Rain chances will be low...with limited moisture
return/instability...dependent upon any impulse that may dive
southeastward in the northwest flow towards the middle of next week.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1240 PM CDT Thursday Jul 24 2014
Eroding precipitation allowing for mixing to the surface on backside with gusty
winds 20 to 40kt. Impact at Fargo for the early afternoon. Otherwise VFR
west/ southeast winds 10-15 gusts 20-25kts through the afternoon. Another round of
convection expected toward morning across dvl and gfk and tvf.