Area forecast discussion
National Weather Service Marquette Michigan
745 PM EDT Tuesday may 21 2013
Short term...(this evening through wednesday)
issued at 357 PM EDT Tuesday may 21 2013
12z roabs/latest WV imagery and RUC analysis show slow moving upper low
over eastern sdakota between upper ridge over scentral Canada and a ridge off
the southeast Continental U.S.. band of rain showers/scattered ts that impacted the County Warning Area earlier has
lifted to the north along with responsible shortwave...allowing for mainly
dry weather over Upper Michigan early this afternoon. But since the County Warning Area is north of surface
warm fnt in WI...plenty of low clouds linger. There is also some fog...
mainly near the cooler Great Lakes. Another disturbance is rotating north
through Iowa around the closed low. The aprch of this disturbance has
resulted in some rain showers over central WI where breaks in the low clouds
along and S of warm fnt have lifted sb cape 500-1000 j/kg per Storm Prediction Center
mesoanalysis.
Main forecast concerns in the short term are rain showers/ts trends associated
with shortwave in Iowa and then aprch of main upper low.
Late this aftn/tngt...short range models are in fairly good
agreement showing rain showers now over central WI drifting across the WI
border by 21z and then continuing to the NE. RUC forecast sdngs modified
for temperature/dewpt of 68/58 yields SBCAPE up to 750 j/kg...so added
mention of ts. Relatively weak winds surface-500 mb as well as deep
moisture/skinny cape with persistent low clouds limiting diurnal heating
indicate a low risk for any severe ts...but any rain showers could result in
some heavy rain with forecast kinx as hi as the upper 30s. Once the rain showers
move farther to the NE and away from the surface heating area...one might
expect these rain showers to diminish through the night. But forecast area of 850 mb-7
fgen north of warm fnt might act to sustain these rain showers. Will go with hi
chance-likely probability of precipitation this evening near the WI border diminishing to chcy
probability of precipitation to the NE. Since the low level flow is forecast to back more to the NE
following the passage of this rain showers area...expect cooler lake
air/some fog to move back into the area overngt.
Wednesday...as closed low to the west begins to shift faster to the east-southeast to SW
WI by 00z Thursday...area of larger scale qvector cnvgc will impact mainly
the area near the WI border but weaken with time as the upper clo
begins to open. Band of rain accompanying axis of sharper fgen over
Western Lake supply/the western zones should thus shift slowly to the southeast through the
day. Arrival of drier air from the northwest to the southeast of expanding hi pressure
over scentral Canada might start to diminish the precipitation over the far west
later in the day. Otherwise...lowered forecast hi temperatures to account for steady
NE wind off lake supply and expected cloud cover.
Long term...(wednesday night through tuesday)
issued at 357 PM EDT Tuesday may 21 2013
After a wet start to the week...the long term period looks to be
fairly dry as Canadian high pressure slides through the upper Great
Lakes region.
First...the upper trough that has been influencing the weather for
the start of the work week will be situated over Wisconsin and Iowa
and shifting east through the Great Lakes region on Wednesday
night. Meanwhile...the surface low will be located over lower
Michigan at 00z Thursday and begin to move up the St Lawrence
seaway Wednesday night into Thursday as a shortwave intensifies the
low. As this occurs...high pressure originating from north central
Canada will be moving a ridge into the upper Mississippi Valley on
Wednesday night and the upper Great Lakes on Thursday. With the
upper trough and close proximity of the low...there will still be
deeper moisture and 850-700mb q-vector convergence over the
southeast half of the County Warning Area. In addition...with the increasing
northerly 850-700mb flow over the area models are consistent on an
area of fgen setup from Ironwood through Eastern Lake Superior at
00z Thursday. Then as the low shifts east...the fgen will slide
southeast through the night and likely exit the most if not all of
the County Warning Area by 12z Thursday. At this point...thinking that the movement
of the precipitation should keep amounts under a quarter of an
inch.
Canadian high pressure then becomes the dominating feature for the
rest of the period...as the area is under northwest flow aloft.
This dry Canadian air and cooler northerly low level winds will
lead to nice but slightly cooler than normal start to the Memorial
Day weekend. The strongest northerly flow off Lake Superior will be
on Thursday with the closer proximity of the exiting low. This will
keep temperatures cooler than most of the days...with highs in the
upper 40s near Lake Superior and in the 50s inland. Friday-Sunday
will be dominated by lake breezes each day...with the warmest
temperatures over the interior locations /60s/. There are hints of a
couple weak shortwaves moving through the northwest flow aloft
Fri-sun...but will the dry air in place...wouldn/T expect much for
precipitation chances. Under the high pressure ridge on Thursday
night...expect to see some sub freezing lows over the interior
portions of Upper Michigan. Precipitable water values around 40 percent of normal
and light winds would be favorable well below normal lows. Mav/met
guidance picking up on this idea with lows between 25-30 over the
west and that seems fairly reasonable. Have trended that direction
and lowered temperatures over the west around 5 degrees. Frost/freeze
headlines Don/T start until Memorial Day...so there won't be any
headlines...but anyone that has planted early will need to prepare
for a potential frost/freeze.
Upper ridging that will be nearly stationary just east of the
northern rockies during this period will begin to shift east on
Sunday night as the upper trough over the New England states shifts
east into the Atlantic. This will start a gradual warming trend
towards Memorial Day and into the first part of next week. In
addition...it will also bring better opportunities for shortwaves
to ride over the ridge and into the area later Monday and more
likely towards Tuesday.
&&
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 745 PM EDT Tuesday may 21 2013
Cool/moist air upsloping off Lake Superior will likely result in
LIFR conditions at kiwd/kcmx/ksaw through the night. Expect -shra at
times along with some -dz. Drier air may begin to make inroads from
the north during the day Wednesday as low pressure that has plagued the area in
recent days continues to weaken and high pressure begins to nose S
toward the upper lakes. If so...kcmx should improve to low MVFR in
the afternoon and kiwd may improve to IFR.
&&
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 357 PM EDT Tuesday may 21 2013
Given widespread area of rain that impacted much of lake supply into this
morning...some recent ship observation that indicated low visibility...and
shallow cool airmass over the lake...opted to extended dense fog
advisory through tonight. Arrival of drier air from the northwest on Wednesday will
slowly diminish the fog. Otherwise...NE winds up to 25 to 30 kts...
with some gale force gusts at the higher platforms...will continue
strongest over Western Lake supply where terrain funneling will enhance
the wind speeds.
Gusty northerly winds are expected behind the low pressure system
on Wednesday night into Thursday...but lingering warm air aloft
should keep winds in 20-25kt range. Then...a high pressure ridge
building southeast over the upper Great Lakes for Thursday night
through the weekend will bring light winds to Lake Superior.
&&
MQT watches/warnings/advisories...
Upper Michigan...
none.
Lake Superior...
dense fog advisory until 6 am EDT /5 am CDT/ Wednesday for
lsz162-243>249-263>267.
Lake Michigan...
dense fog advisory until midnight EDT tonight for lmz221-248-250.
&&
$$
Short term...kc
long term...srf
aviation...rolfson
marine...kc
