Area forecast discussion
National Weather Service Grand Rapids Michigan
158 PM EDT Wednesday may 22 2013
Latest update...
aviation
Synopsis...
issued at 343 am EDT Wednesday may 22 2013
Southwest Michigan will see a wet period starting today and lasting
through middle day Thursday. Low pressure will only slowly move
through the area and this system will provide the persistent showers
along with a few thunderstorms. The rain will come to an end
Thursday afternoon into the evening from northwest to southeast.
Friday will be dry with sunshine returning.
Temperatures will cool off significantly through the rest of the
work week. After highs mainly in the low and middle 70s today...it
will only get into the upper 50s to lower 60s for Thursday and
Friday.
The Holiday weekend into early next week looks dry. Temperatures
will be near normal values...in the upper 60s to middle 70s.
&&
Update...
issued at 1203 PM EDT Wednesday may 22 2013
Upper low is seen spinning across Iowa at midday. A shortwave on
its periphery is rotating toward Southern Lake Michigan. Better
dynamics will come into play this afternoon and evening in terms
of any threat for severe weather as the shortwave rotates by the
area. In addition...models indicate a jet streak that will move
over lower Michigan this afternoon and evening. This will place south
central portions of the state towards Lansing and Jackson in the
right entrance upper divergence region. So...dynamics appear
favorable in the slight risk area especially.
The air mass is beginning to recover a bit at temperatures nudge
to around 70. If we reach the middle 70s with dew points in the middle
60s DTX 12z modified sounding reveals cape values near 2000 j/kg
and Li/S around -5. Some breaks to the south will work in and
provide some heating.
Watching area of storms over northern Illinois/in working in from the
south in the zone of some heating. Also...monitoring weak cells
along the warm front including one that moved from Ionia into
Montcalm County that has acquired weak rotation already.
Expectation is that thunderstorms will become more numerous as we
head through the afternoon and evening and will need to be
monitored for locally heavy rain as well as some marginal severe
weather potential. Some of the strongest storms could produce hail
towards three quarters of an inch and wet microburst winds to
50-60 miles per hour. This obviously hinges upon some additional heating. In
addition...an isolated weak tornado is not out of the question
given bulk shear values around 40 knots and low level easterly
flow near the warm front. The overall threat today is marginal
given weak instability...but will need to be monitored given
decent dynamics.
&&
Short term...(today through friday)
issued at 343 am EDT Wednesday may 22 2013
We will be entering a wet period as a broad area of low pressure...
now centered over SW Wisconsin across the County Warning Area this evening. The
rain should persist into at the first half of Thursday as the
associated cold front moves through.
Despite the increase in precipitation...feel we will largely miss out on
the risk of severe weather today. The best upper forcing from the
right entrance region of the upper jet moves from southern Illinois this
morning...through Indiana this afternoon and into Ohio by evening.
It will be close enough to not totally rule out severe...but chances
this far north look slim. The best instability today stays east of
a mop-btl line...where an isolated severe storm is possible.
Overall however we are largely looking at an expanding area of
showers and embedded thunderstorms that will bring steady rains.
This is already taking place early this morning around the Southern
Lake Michigan region. Pockets of precipitation should gradually become more
widespread by late afternoon into tonight as the deepest moisture
arrives with the low coming in. Precipitable water values remain
between 1.0 and 1.5 inches through today and tonight...so localized
heavy rain will be likely. Localized ponding of water could be an
issue.
The low finally passes east early Thursday with the cold front
coming through into middle day. The steadiest rains should wind down
and rapid drying is indicated from northwest to southeast through the afternoon.
So expect clearing skies over at least the northwest half of the County Warning Area.
Much cooler behind the low for Thursday and Friday with highs each
day only upper 50s to lower 60s. Could be the risk for some patchy
frost Thursday night over the northern two rows of counties inland
from the lake. Winds may remain high enough early on into the night
that temperatures should not fall too quickly. So there may be a small
period...two to four hours...where some frost may occur.
High pressure moves in by Friday keeping US sunny but cool.
Long term...(friday night through tuesday)
issued at 343 am EDT Wednesday may 22 2013
For the most part it looks like a cool and quiet weather pattern for
southwest Michigan through the Memorial Day weekend. The threat of
frost for early Saturday morning continues near and north of Route
10. That frost is thanks to the Canadian polar airmass the moves
into the region Friday and remains in place through Memorial Day.
Light winds...cooler than normal temperatures and dry air will be
the impact of this airmass.
The upper air pattern features an Omega block type pattern across
the United States and Canada through the weekend. Southwest
Michigan is on the down stream side of the large upper ridge. This
will keep US in persistent northwest flow at the jet stream level.
That in turn will keep the warm front from pushing back north
into our area through this forecast period.
Any shortwaves on the southern stream jet will stay south of
Michigan through Tuesday resulting in mostly clear to partly cloudy
skies through the period. A slow warming trend is expected starting
Sunday and continuing through Tuesday.
&&
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 158 PM EDT Wednesday may 22 2013
Convective trends this afternoon along with lower conditions
expected are the main items of interest with this set of forecasts.
More widespread band of rainfall has lifted to the north of the
terminals early this afternoon. Most of the lower ceilings and visibilities
are located with this rain which is near a warm front lifting
through. Scattered showers and storms are developing south of the
main rain band. These can be expected to be possible through
around 00z or so with the diurnal heating.
The rain band should eventually shift south back into the area
later this evening and overnight as the low pressure shifts east
of the area. We are expecting a good deal of IFR conditions with
this band of rain as it moves back into the area. This rain
should be light...but persist into Thursday afternoon. It will likely
move out after this forecast period.
&&
Marine...
issued at 343 am EDT Wednesday may 22 2013
A baggy low will produce light winds today into this evening.
However behind the low northerly winds will increase by late tonight
into Thursday. A Small Craft Advisory will likely be needed by late
tonight. The advisory will probably need to be carried into early
Friday morning until the high moves in and produces lower wave
action.
&&
Fire weather...
issued at 343 am EDT Wednesday may 22 2013
Many areas will see over an inch or more of rain from now through
Thursday. This will producing lowering fire risk.
&&
Hydrology...
issued at 343 am EDT Wednesday may 22 2013
Expect an up tick to the larger river levels with the entire County Warning Area
expected to see between 0.75 and 1.75 inches of rain through
Thursday. However the main Hydro threat will be localized heavy
rain which could produced localized flooding in low lying areas and
also near small creeks and streams.
&&
GRR watches/warnings/advisories...
Michigan...none.
Lm...none.
&&
$$
Update...Duke
synopsis...jk
short term...jk
long term...wdm
aviation...njj
fire weather...jk
hydrology...jk
marine...jk
