Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
146 PM CDT Sat may 25 2013
Short term...(today and tonight)
issued at 344 am CDT Sat may 25 2013...updated for 18z taf
discussion.
Initial shield of warm air advection showers that was depicted well on 310k
isentropic surface on the NAM/GFS is fading away across western WI as this
batch of forcing weakens and dives southeast. In its wake...we have
warm air advection at 850 mb...but the deeper moisture has pushed east...so precipitation has
cut off pretty quick. With the warm air advection and weak moisture
transport...should be able to get some light showers/sprinkles
across Minnesota this morning...but not much more than that.
Best chance for rain today will be across southern Minnesota. Warm front now can
be found across south central Nebraska into NE kan...with a strong low level jet
overrunning it. This has generated an mesoscale convective system over eastern Nebraska this morning.
Thunder starting to increase across Iowa as well as the low level jet has slowly
worked east. Most of this thunderstorm activity will remain south of
Minnesota through the day...but all hi-res models show some of this
moisture from Iowa sneaking up into south central Minnesota through
morning...where some high chance/likely probability of precipitation are continued through
the morning hours. For the afternoon...precipitation looks to shut
off...but we will be stuck with fairly broad cloud cover...with the
only hope for some breaks across the NE mpx County Warning Area thanks to the
influence of a dry surface high that will be splayed out across the
Great Lakes. Given the cloud cover will be a cool day...with
temperatures in south central Minnesota likely staying in the 50s thanks to
better rain chances and thicker cloud cover.
For tonight...all models show another round of convection riding
along north of the warm front...kind of like what we have seen
overnight to our southwest. Question becomes how far north does the
activity make it. Consensus placement from the warm front places it
by 12z Sunday morning from the Black Hills...down through
Yankton...South Dakota and then down to the central Iowa/MO border. Once
again...will see a low level jet overrunning this frontal feature...which
should generate yet another mesoscale convective system. Given the fronts placement to our
southwest...best chances for thunderstorms tonight will be south of
the upper Minnesota river in SW Minnesota into SC Minnesota. For timing...favored highest
probability of precipitation to after 6z...as convection should fire this evening over southeast
sodak into NE Nebraska...then head toward SW/SC Minnesota. All of this activity
would be elevated...so severe threat looks minimal...with the main
impact being the potential for heavy rain...as we have seen this
evening in Nebraska.
Long term...(sunday through friday)
issued at 344 am CDT Sat may 25 2013
The long term period continues to look increasingly wet and
stormy. This is due to the region being sandwiched between a
building upper high along the eastern Seaboard... while a very
deep trough pushes into the western half of the United States.
There should be a round of convection pass across southern Minnesota
Sunday morning...very similar to what has been ongoing overnight
across NE/IA. The storms to our south currently have been basically
sub severe... but very efficient rain producers... with upwards of
1.75 inches of rain in three hours. This is the trend expected
Sunday morning across southern Minnesota... especially the I-90
corridor. Thereafter... a significant diminishing trend in the
precipitation for Sunday afternoon and evening with the nmm/arw
WRF/S in agreement.
Memorial Day is looking a little worse now with even the European model (ecmwf)
driving a wave of convection across the forecast area during the day and
evening. Just general thunder indicated on swody2 which seems
reasonable with the main warm frontal boundary meandering from the
Central Plains to the lower Ohio Valley. Again... the concern will
be localized heavy rainfall. The deterministic runs would also
suggest another round of convection for US late Monday night and
Tuesday morning... especially across southern Minnesota.
This repeating rounds of potential convection is disturbing with
areas of southern and especially southeast Minnesota running well above
normal on rainfall for the month of may. The threat for flash
flooding will be on the increase. It was pointed out on Friday
in the weathertalk from Dr Seely at the umn that since March
1st...(meteorological spring) it has been one of the wettest in
history for many areas of Minnesota. Add this to the cips analogs
for 5 days from now and one sees a very wet pattern across all of
the region with 2 inches of rainfall exceeding 30 percent
probability with even widespread 3 inches having a 10 percent
probability. This is in addition to the rains Sunday through
Tuesday. Not surprising then are the run totals from the GFS and
European model (ecmwf) through next Friday which paint the landscape with 2 to 4
inches of rain... with 4 inches or more south of US. Digressing
for a moment... one of the months/years that has shown up in the
cips analogs recently is July 1993... with record flooding in this
part of the country. A review from ncdc showed low pressure aloft
over the western High Plains with a strong SW jet at 250 mb across
our area. The Bermuda high had pushed into the southeast United
States with organized 850 mb winds from the western Gulf of Mexico
to the western Great Lakes. Hence... the flooding potential is a
big concern for the week ahead as the pattern in the Summer of
1993 mimics our week ahead quite well.
Finally... and just as important... will be the threat for severe
weather next week as the warm front lifts north into our area
beginning on Tuesday. Not too concern about severe on Sunday. The
chance increases some on Monday (isolated)...especially if
afternoon convection develops as deep layer shear rises. Then from
Tuesday Onward there is severe potential each day. The cips
analogs contain many severe reports for US for the middle of next
week with severe probabilities from 15 to 30 percent for the
entire forecast area using the top 8 analogs. A cold front may move across
the forecast area from Friday into Saturday...diminishing the severe weather
threat.
&&
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 100 PM CDT Sat may 25 2013
Remnants of mesoscale convective system which produced moderate to heavy amounts of
precipitation over much of northern Iowa...and lighter amounts
above far southern Minnesota continues to decrease in coverage and
intensity as it treks into northern Illinois. Closer to home...large
swath of strato-cumulus continues to blanket all of the taf region.
Western half of this region dealing with MVFR...to low end
MVFR ceilings...with VFR conditions elsewhere. Although infrared satellite
confirming some redevelopment of lower ceilings over eastern sodak
..loss of heating by early this evening should give green
light to short term loss of ceilings over kaxn...kstc...and krwf
..with redevelopment possible later this evening ahead of
area of convection forming over central Dakotas after 03z.
Nothing very substantial concerning forcing in respect to
convection during the next 24 hours or so...save tonight
over west central through south central Minnesota. With that said
tempo groups will be the rule at most western taf locations
with instability parameters indicating possible short term
thunder at krwf. Light to MDT southeast flow will continue for much of
the forecast period. VFR visibilities will be seen into Sunday afternoon
..minus short periods of MVFR associated with possible convection.
VFR ceilings expected at all Airport locations after 15z.
Kmsp...
Confidence is not high for shower activity later this evening.
Moderate Theta-E advection and very potent 250mb divergence
Couplets after 06z...could generate a passing shower at kmsp.
Much better bet concerns fairly drastic lowering of VFR to
MVFR ceilings by 23z time period. Actually have a fairly large
area of low MVFR ceilings over west central WI at this time advecting
in this direction. Heating should elevate ceilings as they proceed
east. Although current forecast depicts contuinuation of MVFR ceilings
through 15z...there is a possibility of a short term break in
the cloud cover mentioned above between 03z and 05z. After 15z
MDT southeast flow and VFR ceilings and visibilities should be anticipated until
end of period. Better chances for convective activity will
be encountered by late Sunday night.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...mpg
long term...rah
aviation...ajz
