Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
936 PM CDT Tuesday may 5 2015
issued at 936 PM CDT Tuesday may 5 2015
Continued the trend of delaying the higher probability of precipitation. Will likely see
surges of scattered showers entering the southern forecast area...attempting
to stay alive until they reach Canada...but likely dissipating as
they outrun the stronger forcing. The more widespread showers
should occur Wednesday afternoon into the evening hours as the upper low
is closer to the region.
Update issued at 644 PM CDT Tuesday may 5 2015
Slowed down the higher probability of precipitation until more after 12z...and even that
may not be slow enough. According to the latest rap/hrrr there
will be an initial band of showers (now across south dakota) that
moves into North Dakota around midnight...but eventually dissipates
as it moves into a drier airmass. The more widespread rain will
likely occur/move into the region after 12z in association with a
stronger 850mb jet. The latest rap suggests this may not occur
until after 15z across the southern forecast area...and even later across the
northern forecast area. If these model trends hold over the next several
hours will consider updating probability of precipitation further with the 9pm-10pm
update. It is going to rain...but this rain may be delayed a bit.
Short term...(this evening through Wednesday night)
issued at 305 PM CDT Tuesday may 5 2015
The main forecast challenge will be the rain moving in late
tonight and holding over the area through Thursday night. As for this
afternoon...still remaining mostly sunny with temperatures in the 70s.
Actually seeing a 40f dew point value now at Elbow Lake...so the
moisture is slowly expanding northward. Will see the clouds
expanding south to north tonight as well with the slowly rising
dew points. Should be a little warmer across the south for these
reasons. The gusty S-southeast winds should taper off a bit overnight so
the dangerous fire conditions should abate by early evening. The
next wave over the southwest United States will continue to lift
up toward the area tonight with steady south winds. How fast any
precipitation actually makes it into the forecast area will be the main question.
Models really do not show a lot of forcing tonight and therefore
will probably not see much precipitation actually reaching the ground until
closer to Wednesday morning. Will leave low precipitation chances south of
Interstate 94 to blend with adjacent offices. See a much better
push of 850mb winds on Wednesday helping to continue the moisture surge.
Not a lot of instability through the day but will leave the
mention of isolated thunder. Surface low tracks up toward kabr by 12z
Thursday with models indicating somewhat of a dry slot to the SW. Still
some weak instability over the area so will keep the showers with
isolated thunder wording.
Long term...(thursday through tuesday)
issued at 305 PM CDT Tuesday may 5 2015
Surface boundary will slowly push from west to east on Thursday as well
with gusty northwest winds picking up behind it. Models disagree
on how fast the precipitation will end with the 12z NAM lingering heavier
amounts of precipitation the longest. Therefore its storm total precipitation is
much heavier than the other models. Other solutions show half inch
to one inch amounts with a little more or less in some areas.
After the precipitation ends Thursday night it looks noticeably cooler for Friday.
For Friday night through Tuesday...main feature of interest will be
next upper low models forecast to lift into the forecast area later Sunday
into early next week. Differences of course however looks like
another potential for respectable rainfall across at least a
portion of the forecast area dependent on surface low track. Dry
and relatively cool conditions initially in period with rain
chances increasing later Sunday as associated surface low lifts
northeast. With differing solutions chance probability of precipitation seem reasonable at
this point. Minimal T potential through the period. Temperatures
through the period will range below average.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 644 PM CDT Tuesday may 5 2015
Much of the overnight hours will remain VFR. MVFR (possibly ifr) ceilings
will invade the region from south to north Wednesday morning. -Ra
will become more widespread late Wednesday morning and afternoon.