Area forecast discussion
National Weather Service Marquette Michigan
410 PM EDT Tuesday Jun 18 2013
Short term...(this evening through wednesday)
issued at 409 PM EDT Tuesday Jun 18 2013
WV imagery and RUC analysis indicated northwest middle/upper level flow
through the northern Great Lakes between a trough over Quebec and a ridge
from The Rockies into the Western Plains. At the surface...a ridge extended
from James Bay to Lake Superior. With the dry airmass over the
region (pwat around 0.50 or about 50 percent of normal)...a weak
shortwave trough into Western Lake Superior only supported a patch of
middle/high clouds.
Tonight...high pressure will continue to dominate the region keeping
conditions dry under mostly clear skies. As the ridge axis slides southeast
overnight...light return srly flow will result in a bit more mixing
especially over the far west and along the Lake Superior shoreline.
Look for min temperatures to range from around 40 inland to the middle
to upper 40s along the Great Lakes shorelines.
Wednesday...as the ridge slowly slides off to the east...srly winds
will increase. 850 mb temperatures around 10c and mixing to around 800 mb
will support temperatures into the middle 70s inland...except near Lake
Michigan where onshore flow keeps readings in the 60s. Although
moisture will also increase slightly...the higher low level Theta-E
axis to support rain showers/thunderstorms and rain with weak shortwaves in northwest flow is expected
to remain west of the County Warning Area.
Long term...(wednesday night through tuesday)
issued at 409 PM EDT Tuesday Jun 18 2013
Area will be under northwest flow aloft to start the period as the
upper Great Lakes is on the eastern side of the ridge over the
northern plains and upper Mississippi Valley. A weak shortwave will
be sliding across Northeast Lake Superior on Wednesday night...while
a surface trough drops southeast across the County Warning Area during the overnight
period. There will likely be some showers and a few thunderstorms
with this trough on Wednesday night and will follow a general
consensus for the timing of the probability of precipitation as it moves in.
This front looks to stall across Upper Michigan on Thursday and
will combine with developing lake breezes to produce afternoon
showers and thunderstorms. The strength of these thunderstorms will
depend on the amount of diurnal heating...increasing southerly
flow with a developing warm front on the boundary...and the arrival
of the another weak shortwave during the late afternoon and
evening. Ml cape values of 500-1000 j/kg over the western 2/3rds
of the County Warning Area and 0-6km bulk shear values around 30kts supports
thunderstorms and some tilting of the updrafts. Heavy rain and
small hail will be the primary threats...as ncape values around .1
should keep any hail from growing too large. Will continue to
highlight the highest probability of precipitation over the interior west/central...closest
to Lake Superior lake breeze and then follow the storm motion to the
southeast.
Thursday night through the weekend is shaping up to be a fairly
active pattern for thunderstorms in the upper Mississippi Valley
and upper Great Lakes region. This is due to the upper ridge
gradually shifting east into the upper Great Lakes.
Meanwhile...weak surface low will remain fairly stationary over the
central/northern plains. From this low...a warm front will looks to
setup from the stalled trough on Thursday and remain located around
the upper Great Lakes region through the weekend. Looking at this
large scale pattern...it is very conducive periods of showers and
potentially strong thunderstorms. But trying to pin down the
exact location and timing is difficult due to the variability of the
shortwaves and position of the warm front. Instability will
gradually grow from Friday into the weekend...as persistent
southwesterly flow ahead of the low pulls plenty of Gulf moisture
into the area. Using ml cape values to remove some of the low
level moist biases in the models for Friday into the weekend...there
are still some decent values for u.P. Standards. Friday they look to
peak in the 750-1500 j/kg range over the west and then grow to
1500-2500 j/kg for Sat/sun depending on the model. The GFS is the
most aggressive on the northward extent of the warm front...while
the Gem/European model (ecmwf) try to keep the front a touch south of the area. It
will probably be a variety of thunderstorm types during that period.
Convective complexes moving east /via forward prop corfidi vectors/
around the ridge will likely be the main threat...but with the
instability present and limited inhibition...diurnal thunderstorms
will also be possible. The only concerns would be if the ridge and
warm front build far enough north to slide most of the thunderstorm
complexes north of Upper Michigan or the more likely scenario of it
becoming hung up south of the area /especially as convection holds
them south/. With the growing confidence...will add a mention of
strong thunderstorms for the weekend in both the severe weather potential statement and ehwo. Heavy
rain is also possible during this period with the thunderstorms...as
precipitable water values rise above 1.5 inches which is well above the 75th
percentile for climatology for this area.
It will be pretty humid for Friday into the weekend /dewpoints in
the upper 50s and 60s/ and the temperatures will depend on the
positioning of the warm front. Will continue to show temperatures in the
middle 70s to lower 80s for most locations...with the warmest values
near the Wisconsin border. If the GFS ends up being correct...would
have to bump temperatures up well into the 80s for the end of the weekend.
Uncertainty really grows heading into Monday/Tuesday...as a lot
depends on the weekend weather. The general idea from the models is
that the ridge breaks down and the area will be under zonal flow
aloft. This will continue to bring waves across the area and keep
the thunderstorm potential in place for that period. At this
time...models are indicating a cold front dropping south out of
Canada on Wednesday...which may bring an end to the warm/humid
weather.
Finally...will continue to mention patchy fog developing on Lake
Superior on Wednesday night and then continuing into early next
week. Will likely need to expand it to areas or even dense fog as it
nears. Also...added a mention of fog over Lake Michigan nearshore
areas starting late Thursday night as the precipitation and higher
dewpoints start to affect that area.
&&
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 133 PM EDT Tuesday Jun 18 2013
With high pressure in control...VFR conditions expected to continue
through the period.
&&
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 409 PM EDT Tuesday Jun 18 2013
No significant pressure changes through the period will result in
winds below 25 knots...outside of any thunderstorms which are possible
from Wednesday night through Sunday. Increasing low level moisture
into the region from after Wednesday...will result in areas of
fog...possibly dense at times.
&&
MQT watches/warnings/advisories...
Upper Michigan...
none.
Lake Superior...
none.
Lake Michigan...
none.
&&
$$
Short term...jlb
long term...srf
aviation...jlb
marine...jlb
