Bill Schintler
EF4
A weak storm system will bring some very light precipitation to the area after midnight tonight. A more significant winter storm will affect the area starting late Thursday afternoon. It appears as through the heaviest snowfall totals will remain well north of the Cedar Rapids area. Below are forecasts for specific locations in eastern IA for the storm starting Thursday.
Cedar Rapids (Eastern IA Airport):
Rain will start at 4:30 PM on Thursday. Rain will change to snow at 6 AM Friday and accumulate to 1.5 inches before ending Friday afternoon.
Iowa City:
Rain will start at 6:00 PM on Thursday. Thunder will be possible in the evening. Rain will change to snow at 9 AM Friday with little or no snowfall accumulation before ending Friday afternoon.
Marengo:
Rain will start at 5:30 PM on Thursday. Thunder will be possible in the evening. Rain will change to snow at 8 AM Friday and accumulate to 0.5 inches before ending Friday afternoon.
Coggon and Paris:
Rain will start at 4:15 PM on Thursday. Rain will change to snow at 5 AM Friday and accumulate to 2.5 inches before ending Friday afternoon.
Synopsis:
00Z analysis showed a weak wave diving SE through SD towards IA and a stronger H5 S/WV entering the PAC NW with 50m 12hr height falls concentrated over the Puget Sound region. Light radar returns over WRN IA were associated with the first wave however only a few SFC locations reported light precipitation. Latest MDL runs have come into better agreement now that the system has come on shore and is better sampled. Previous runs of the NAM and UKMET were too far N with the track of the SFC and H85 lows, while the ECMWF and GFS had favored a more SRLY track. The NAM now has less NRLY bias compared with the global MDLs, with the main remaining difference being that the GFS is about 6 hours slower with the progression of the SFC low through 06Z Friday. Will side with the GFS.
Discussion:
Tonight - forcing is impressive with this system, however lowest condensation pressure deficits will occur after strongest UVM decreases. Therefore, most of the forcing and lift will go into cloud production and any precipitation will be very light.
Thursday through Friday – a vigorous storm system will bring a variety of precipitation to the area. By Thursday evening, a 60kt LLJ really cranks up and focuses into IA as a zone of strong isentropic lift along 290-305K SFCs moves from SW to NE across the state between 00Z and 06Z. Elevated convection is possible N of the H85 WF in an area between US-34 and US-30 in ERN IA. Impressive QPF amounts are indicated, with totals between 0.25 to as much as 1 inch. Now for the hard part: what areas will be cold enough for snowfall for the duration of the event? A sharp transition between liquid precipitation and frozen will exist somewhere around US-20 during the period over which the heaviest precipitation is falling, and this makes for a difficult forecast for snowfall totals. H85 CAA holds off until the H85 low moves E of the area, which will keep areas S of US-20 in liquid precipitation until early Friday morning.
[FONT="]- [/FONT]bill
2:00 AM CDT 03/20/08
Cedar Rapids (Eastern IA Airport):
Rain will start at 4:30 PM on Thursday. Rain will change to snow at 6 AM Friday and accumulate to 1.5 inches before ending Friday afternoon.
Iowa City:
Rain will start at 6:00 PM on Thursday. Thunder will be possible in the evening. Rain will change to snow at 9 AM Friday with little or no snowfall accumulation before ending Friday afternoon.
Marengo:
Rain will start at 5:30 PM on Thursday. Thunder will be possible in the evening. Rain will change to snow at 8 AM Friday and accumulate to 0.5 inches before ending Friday afternoon.
Coggon and Paris:
Rain will start at 4:15 PM on Thursday. Rain will change to snow at 5 AM Friday and accumulate to 2.5 inches before ending Friday afternoon.
Synopsis:
00Z analysis showed a weak wave diving SE through SD towards IA and a stronger H5 S/WV entering the PAC NW with 50m 12hr height falls concentrated over the Puget Sound region. Light radar returns over WRN IA were associated with the first wave however only a few SFC locations reported light precipitation. Latest MDL runs have come into better agreement now that the system has come on shore and is better sampled. Previous runs of the NAM and UKMET were too far N with the track of the SFC and H85 lows, while the ECMWF and GFS had favored a more SRLY track. The NAM now has less NRLY bias compared with the global MDLs, with the main remaining difference being that the GFS is about 6 hours slower with the progression of the SFC low through 06Z Friday. Will side with the GFS.
Discussion:
Tonight - forcing is impressive with this system, however lowest condensation pressure deficits will occur after strongest UVM decreases. Therefore, most of the forcing and lift will go into cloud production and any precipitation will be very light.
Thursday through Friday – a vigorous storm system will bring a variety of precipitation to the area. By Thursday evening, a 60kt LLJ really cranks up and focuses into IA as a zone of strong isentropic lift along 290-305K SFCs moves from SW to NE across the state between 00Z and 06Z. Elevated convection is possible N of the H85 WF in an area between US-34 and US-30 in ERN IA. Impressive QPF amounts are indicated, with totals between 0.25 to as much as 1 inch. Now for the hard part: what areas will be cold enough for snowfall for the duration of the event? A sharp transition between liquid precipitation and frozen will exist somewhere around US-20 during the period over which the heaviest precipitation is falling, and this makes for a difficult forecast for snowfall totals. H85 CAA holds off until the H85 low moves E of the area, which will keep areas S of US-20 in liquid precipitation until early Friday morning.
[FONT="]- [/FONT]bill
2:00 AM CDT 03/20/08
