Area forecast discussion
National Weather Service Marquette Michigan
402 PM EDT Wednesday may 22 2013
Short term...(this evening through thursday)
issued at 353 PM EDT Wednesday may 22 2013
12z radiosonde observations/latest WV imagery and RUC analysis show sluggish upper low
over the upper MS River Valley between ridge off the southeast Continental U.S. And another
ridge axis over The Rockies. Band of -shra stretching from NE Minnesota into
the western County Warning Area under band of 850 mb-7 fgen to the NE of the closed low is
holding firm even though low level dry air is surging into NE Minnesota/Western Lake
supply in steady NE flow between hi pressure over northern Manitoba and surface low pressure
in the lower lakes. Another larger area of rain showers/isolated ts over the southeast
half of WI/S half of Lake Michigan is expanding to the north as shortwave over
Illinois/left exit region of supporting 300 mb jet maximum is moving north of the
closed low. Otherwise...low clouds have been quite persistent over Upper Michigan
with chilly NE wind off lake supply. Some fog has persisted as well near
lake supply east of the Keweenaw...where the low level dry air has not yet
arrived.
Main forecast concerns in the short term involve how drier air arriving
from the north will impact probability of precipitation associated with band of fgen over the western
zones and area of rain showers moving north toward the southeast counties.
Tonight...upper low now over southeast Minnesota is prognosticated to drift east-southeast...and NAM shows
band of 850 mb-7 fgen/h85-5 qvector cnvgc following this feature southeastward
across mainly the west half of the County Warning Area. At the same time...h7-3 qvector
cnvgc/upper dvgc in left exit ahead of shortwave/supporting upper jet
lifting north-northeastward will impact mainly the southeast counties. Looks like these
dynamics may interact for a time late this afternoon/early evening over the
southeast zones. So higher probability of precipitation in this area at that time seem appropriate. At
the same time...drier air surging into the northwest County Warning Area under stronger north-northeast
flow will end any lingering precipitation as fgen axis shifts to the southeast. The
precipitation will end even over the southeast zones after 06z following departure of
shortwave/accompanying dynamics and arrival of drier low level air. The
arrival of the drier low level air and exit of the dynamics will allow for
some clearing...but the upslope north-northeast flow may slow the process over the
higher terrain near lake supply.
Thursday...hi pressure is forecast to build into the upper lakes...resulting in dry weather.
Although lingering 850 mb thermal trough with temperatures around 0c through 00z
would indicate quite a bit of diurnal cumulus/SC at this time of year
over land...dryness of incoming airmass as well as low level anti-cyclonic/
diffluent flow will result in mostly clear skies. If there is any upslope SC
over the higher terrain near lake supply...this cloud will mix out early. The
forecast 850 mb temperatures and mixing to 800 mb-85 on NAM forecast sdngs yields hi temperatures
topping out in the 50s over the interior. But stiff north-northeast wind off lake
supply will cause temperatures to hold in the 40s near The Big Lake. These
stronger NE winds will diminish over the west in the afternoon with the aprch
of the hi center/weakening pressure gradient.
Long term...(thursday night through wednesday)
issued at 353 PM EDT Wednesday may 22 2013
Slow moving and rather stable upper air pattern expected through the
entire length of the long term. Initially late this week...there is
a trough over Pacific northwest with ridging over central Continental U.S....
and troughing over much of eastern Canada across the Great Lakes.
Expect below normal temperatures to prevail through the Holiday
weekend as the trough only slowly moves to the east. Eventually...
warmer temperatures are expected by middle of next week when ridging
expands from plains across the Great Lakes. After an unsettled and
wet week that has occurred over the upper Great Lakes...Hudson Bay
high pressure ridging across the Great Lakes should bring a
prolonged period of dry weather into next week. Certainly possible
this dry weather stretch may even persist into the middle of next
week. Warm front forming to the south and west of Upper Michigan
will result in some smaller chances of precipitation by next Wednesday...
but given the very dry airmass in place...greatest chance of showers
and storms will likely stay to west of upper lakes closer to axis of
higher 850 mb-700 mb moisture and instability.
Gusty winds around on Thursday diminish by the weekend as high
pressure building south out of northern Ontario becomes more
established. Lighter winds on Thursday night and very dry airmass
overhead due to strong mixing earlier in the day will support min
temperatures dropping to around 20 degrees interior west and in the 20s to
lower 30s elsewhere. Expect widespread frost for many areas on
Thursday night. We do not officially begin the frost and freeze
headlines until Memorial Day but will continue to include mention in
the grids. With strong high pressure over the area...near 1030mb...
lake breezes may get gusty at times this weekend. After a cooler day
all areas on Friday...cooling will become more of a Lakeside feature
through the weekend as inland areas rise into the 60s.
Seems there is a slim chance of light rain/sprinkles over far West
County warning area late Friday night into Saturday morning. 12z NAM soundings show
moisture in middle levels enhanced by right entrance region of
departing jet streak over Ontario building down enough along with
sufficient uvm to result in band of light rain showers making it into iwd
06z-12z on Saturday. European model (ecmwf)/GFS show some middle level moisture but have
quantitative precipitation forecast staying out of County Warning Area. 12z European model (ecmwf) does show a bit now though. NAM
seems too aggressive with eastward push of light precipitation so will not
put a mention in yet. Increase in clouds overnight will impact min
temperatures and may restrict potential for frost...at least in the
interior West County warning area. Elsewhere...temperatures dropping into the upper 20s or
near 30 degrees will support more frost...especially inland from the
lakes. If there are broken clouds west...they should dissipate by
Saturday evening resulting in another cool night with some frost
inland from the Great Lakes shores.
Due to cool and damp weather and moderate rain amounts in some areas
/had report today of over 4 inches to west of Ontonagon/...fire
weather issues are taking a brief hiatus. Eventually due to almost a
week of drying...increasing south/southwest winds...and warmer
temperatures into the 70s early-middle next week may see increasing
fire weather concerns for areas that have not experienced a full
green up and/or seen a lot of rain over the last few days. &&
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 123 PM EDT Wednesday may 22 2013
As a steady north-northeast wind between hi pressure in scentral Canada and low pressure
over the lower Great Lakes advects much drier low level air over Upper Michigan...
expect improving conditions to VFR this evening. Cmx will be closer to
the incoming drier air and see a quicker improvement than at iwd/
saw...where a more sgnft upslope wind component will also slow the
trend toward VFR. Under a tightening pressure gradient...expect gusty
north-northeast winds at all 3 sites tonight/Thursday morning.
&&
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 353 PM EDT Wednesday may 22 2013
Expect increasing NE winds up to 25-30 kts under sharpening pressure
gradient in advance of hi pressure building toward lake supply through
tonight. This strengthening flow will advect drier air over the
lake...so lingering fog should dissipate this evening. Based on
current visibility reports/webcam imagery near the lake...opted to
canx going dense fog advisories that were set to expire at 21z.
Closer approach of hi pressure/weaker pressure gradient will result in
slowly diminishing winds west to east on Thursday. As high pressure continues to
spread across the upper Great Lakes through the weekend...expect
winds less than 20 kts on Lake Superior. Lighter winds will continue
into early next week.
&&
MQT watches/warnings/advisories...
Upper Michigan...
none.
Lake Superior...
none.
Lake Michigan...
dense fog advisory until 6 PM EDT this evening for lmz221-248-
250.
&&
$$
Short term...kc
long term...jla
aviation...kc
marine...kc/jla
