Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
410 am CDT Wednesday may 22 2013
Short term...(today and tonight)
issued at 410 am CDT Wednesday may 22 2013
Cool and cloudy with light rain showers will be the story today.
Most of the forecast area is in the upper 40s to lower 50s with damp
conditions and a northeasterly breeze early this morning...so it is
definitely jacket weather out there. We cooled temperatures today by
a couple degrees from the previous forecast in order to keep most of
the area in the 50s for highs...the exception would be portions of
west central WI which should be a few degrees warmer. There is very
little temperature advection today and with the lingering clouds and
light rain in the forecast...we might only be able to warm 6-8
degrees from where temperatures stand now. Yesterday...St.Cloud only
hit 50 degrees for a high given the cooling from the nearly 0.50" of
rain that fell. The rain won't be nearly as heavy today...but the
temperatures will still suffer and there may actually be slightly better
light rain/shower coverage today. There is a back edge to the cloud
cover in northern Minnesota which means there will be nice diurnal
warming across the northern half of the state by this afternoon. If
the cloud clear before or around the noon hour in central Minnesota...the
we will likely be too low with temperatures across northern portions of the
forecast area. However...the clearing trend does mean we have high
confidence in the rain moving out tonight. The dewpoint depressions
/outside of the lower boundary layer/ off the model forecast
soundings show nice drying after midnight.
The only other forecast concern is for the potential for a little
fog early this evening immediately after the clouds clear. It is not
a big concern through because we are quickly advecting in drier air
from the northeast as we head toward Thursday morning. We left the
fog out for now. We also kept the thunder out of the forecast today
even though isolated thunder is still possible across Iowa/WI and
southeast Minnesota. We just don't have the instability to be concerned too
much with this. In fact...we even entertained the idea of changing
the weather from light rain showers to sprinkles/drizzle today. It
all amounts to the same thing...cool and damp.
Long term...(thursday through tuesday)
issued at 410 am CDT Wednesday may 22 2013
The period begins with our pesky low pressure system finally to
our southeast along with a substantial Canadian high pressure
system building south across the upper Mississippi Valley region.
Thursday and much of Friday will be fine weather days for the forecast area.
The main concerns during this period center around very low
dew points Thursday afternoon leading to min relative humidity values near 20
percent in our WI County Warning Area as well as the threat for some frost/freeze
conditions...again mainly in our WI counties Thursday night/Friday
morning. Used the mix down dew point tool as a start for Thursday
afternoon along with some consraw/consmos. This brought dew points
well down into the 20s over the aforementioned area. The high
pressure system will be nearly overhead Thursday night. With light
winds...a clear sky and dry air in place...lows near freezing
indicated around Ladysmith with middle 30s as far west as the
Minnesota/WI border and well as to the north of the Twin Cities.
Indicated frost in varying degrees of coverage starting with lows
36 degrees or colder.
Beginning with Friday is where things start to slowly unwind with
model consistency. The NAM at this point is the fastest on Friday
on bringing back showers and some thunderstorms across much of the
Minnesota County Warning Area on Friday as moisture and instability begin to increase on
the backside of the high. The Gem/GFS and Euro would keep all but
the far west dry. Therefore...removed the mention of probability of precipitation in the
12z-18z time frame and kept the 18z-24z probability of precipitation confined to the far
west. The Gem/GFS/Euro then indicated scattered showers and
thunderstorms across much of the forecast area Friday night and Saturday.
Probabilities for measurable precipitation are least in the far
eastern WI counties. Nothing too significant (rainfall/severe
weather) expected at this time as small ripples in the upper flow
migrate northeast out of a large upper trough in the western
United States.
Progressing deeper into the Holiday weekend shows two camps
through Memorial Day. The GFS is wet across US Sunday and Monday
while the Euro is basically dry. The difference is seen in the
upper pattern. The pesky upper low that has tormented US for the
past five days reaches the eastern Seaboard by Friday and deepens
as more energy drops into it from the north. The Euro is deepest
and slowest with this feature which actually builds the surface
high back west for a time late in the weekend. The Gem does not
have an upper low and allows for more progression of the upper
pattern and plenty of rainfall. Hence...chances probability of precipitation indicates for
many periods of the extended forecast due to the blended guidance.
The cips analogs were looked at overnight to see what sort of severe
weather occurred with our pattern ahead. Using the 144 hour
analog guidance showed all forms of severe weather with the most
clustering over South Dakota/NE/KS/IA with some severe weather reports over
far western and far southern Minnesota. This correlates well with the GFS
having low pressure forming during this period over the Central
Plains with a warm front meandering to the lower Ohio Valley. The
Euro would be a little slower. So we may Dodge severe weather
during the weekend...but the threat will be on the increase by the
middle of next week as the low pressure system and warm front
advance into the northern plains and upper Mississippi Valley
region.
High/low temperatures will be mainly below normal through the
weekend with a climb back above for early next week.
&&
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1056 PM CDT Tuesday may 21 2013
Occluded system will be slow to move out of the area. Appears the
northeast portion of the area will remain driest...with northeast
flow trying to draw in somewhat drier air. Still looks good IFR
conditions continuing through the night most areas. Kaxn will be
on the edge to the northwest and krnh and Keau to the east. Light
rain and drizzle appears most likely as the system moves through.
As the upper low drops southeast...could see more steady rain
develop to the southeast into the afternoon. Ceilings should gradually
improve to MVFR late in the morning northwest and then clear out
during the evening as the surface ridge begins to move in. This
clearing trend expected to continue to kmsp after 05z//Thu. North
northeast winds during the period...becoming gusty in the morning
out west.
Kmsp...light rain/drizzle remains on the edge across the filed.
This may continue into early morning before main upper circulation
drops southeast into the region...mainly after 10z. Will continue
the IFR ceilings as well...gradually improving late morning/early
afternoon...as main light rain area drops to the southeast.
Clearing trend into the evening...with sky clear developing after
06z/Wed. Northeast to north winds during the period...may become a
bit gusty in the afternoon. Should diminish overnight as the
surface ridge builds southeast.
/Outlook for kmsp/
Thursday...VFR conditions expected. Northeast wind 5 to 15 knots.
Thursday night...VFR conditions expected. East wind less than 10
knots becoming southeast. Friday and Friday night...VFR conditions
expected. Southeast wind 5 to 15 knots. Saturday...MVFR ceilings and
visibilities possible with a chance of showers and thunderstorms.
Southeast wind 10 to 20 knots.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...clf
long term...rah
aviation...dwe
