Bill Schintler
EF4
A moderate winter storm will bring a few inches of new snow to most areas of eastern Iowa beginning early Friday morning. Below are forecasts for specific locations followed by the discussion.
Cedar Rapids:
Snow will start at 5:00 AM Friday. Expect a total accumulation 3.0 inches before the precipitation winds down during the afternoon.
Iowa City:
Snow will start at 3:45 AM Friday. Expect a total accumulation 4.0 inches before the precipitation winds down during the afternoon.
Marengo:
Snow will start at 3:30 AM Friday. Expect a total accumulation 3.5 inches before the precipitation winds down during the afternoon.
Coggon:
Snow will start at 5:10 AM Friday. Expect a total accumulation 2.5 inches before the precipitation winds down during the afternoon.
Synopsis:
The recent active WX pattern will continue as one system exits the Upper-Midwest and an upstream system is taking shape over the SWRN CONUS. Latest MDLS, SFC OBS, and WV imagery all indicate that the H5-H3 system is verifying about 50 mi N then earlier depicted or anticipated. Subjective 00Z UA analysis indicates 110kt H5 streak rounding base of deepening trough over SRN NM. H5 height fall bulls-eye of 150m was located over NM, indicating substantial digging with little EWD motion. A 40kt LLJ is developing over ERN TX, and this will serve as a NWD moisture transport overnight as H85 dewpoints climb to -4C over ECNTL IA and the column quickly saturates by 10Z. The SFC system is taking shape over the SRN high plains with disorganized low-pressure centered W of AMA at 02Z along a sharp baroclinic zone. Further N, widespread light snow is now falling from ERN CO into the TX panhandle in an upsloping regime.
Discussion:
Moderate to strong forcing, possible isolated convective elements, and decent moisture availability will be offset by rapid storm movement, which will help to keep snowfall totals at bay. The system will be a fast mover, with the H85 low initially tracking slowly EWD along I-40 near AMA between 00 and 06Z, and then quickly accelerating to the NE during the morning hours. The H85 low will be centered over MCI by 12Z, and then 50 mi SE of DVN by 18Z. This brings a line parallel to and 80 mi NW of the H85 track right along I-80 in ERN IA during the late morning hours. Concerning the SFC solution, the GFS is somewhat of an outlier, which takes the strongest H8-H7 UVM between 12-18Z too far S, and will lean towards the NAM, ECMWF, UKMET, and NGM. The consensus takes the SFC low along a path from ERN MO to CNTRL IL into SRN MI.
For the most part, the precipitation should be broadly forced. However, the latest mesoscale MDL trends have indicated some weak H7 frontogenetic signatures along with a moderate thermal gradient, with regions of instability possible above that layer. Verification of such would result in localized heavier snowfall totals. Latest trends have also suggested stronger lift in the dendritic growth layer as compared to previous MDL output which showed less dendritic UVM and snow ratios. PROGS indicate stronger QG convergence and ULVL PVA as a the left-exit region of a 120kt H5 speed max ejects from the base of an increasingly negatively-tilted trough. From 12 to 16Z, impressive isentropic lift is noted on the 280-285K SFCS, and a weak TROWAL feature is indicated on the 290K SFC, both of these features strongest between 50 mi S of I-80. Regarding snowfall totals, the Garcia method was investigated using the 285K SFC, this supports 12hr snowfall totals in excess of 5 inches between I-80 and US-30 in SERN IA, with lesser amounts to the N and S. Looking at NAM QPF, 0.3 inches is indicated, while the Cobb algorithm suggests 12:1 to 14:1 ratios.
Looking ahead… In the wake of Friday’s system, the ULVL pattern will transition towards an increasingly zonal flow as H85 WAA spreads into the upper-Midwest and return flow commences at the SFC.
- bill
[FONT="]8:55 PM CST, 12/27/07[/FONT]
Cedar Rapids:
Snow will start at 5:00 AM Friday. Expect a total accumulation 3.0 inches before the precipitation winds down during the afternoon.
Iowa City:
Snow will start at 3:45 AM Friday. Expect a total accumulation 4.0 inches before the precipitation winds down during the afternoon.
Marengo:
Snow will start at 3:30 AM Friday. Expect a total accumulation 3.5 inches before the precipitation winds down during the afternoon.
Coggon:
Snow will start at 5:10 AM Friday. Expect a total accumulation 2.5 inches before the precipitation winds down during the afternoon.
Synopsis:
The recent active WX pattern will continue as one system exits the Upper-Midwest and an upstream system is taking shape over the SWRN CONUS. Latest MDLS, SFC OBS, and WV imagery all indicate that the H5-H3 system is verifying about 50 mi N then earlier depicted or anticipated. Subjective 00Z UA analysis indicates 110kt H5 streak rounding base of deepening trough over SRN NM. H5 height fall bulls-eye of 150m was located over NM, indicating substantial digging with little EWD motion. A 40kt LLJ is developing over ERN TX, and this will serve as a NWD moisture transport overnight as H85 dewpoints climb to -4C over ECNTL IA and the column quickly saturates by 10Z. The SFC system is taking shape over the SRN high plains with disorganized low-pressure centered W of AMA at 02Z along a sharp baroclinic zone. Further N, widespread light snow is now falling from ERN CO into the TX panhandle in an upsloping regime.
Discussion:
Moderate to strong forcing, possible isolated convective elements, and decent moisture availability will be offset by rapid storm movement, which will help to keep snowfall totals at bay. The system will be a fast mover, with the H85 low initially tracking slowly EWD along I-40 near AMA between 00 and 06Z, and then quickly accelerating to the NE during the morning hours. The H85 low will be centered over MCI by 12Z, and then 50 mi SE of DVN by 18Z. This brings a line parallel to and 80 mi NW of the H85 track right along I-80 in ERN IA during the late morning hours. Concerning the SFC solution, the GFS is somewhat of an outlier, which takes the strongest H8-H7 UVM between 12-18Z too far S, and will lean towards the NAM, ECMWF, UKMET, and NGM. The consensus takes the SFC low along a path from ERN MO to CNTRL IL into SRN MI.
For the most part, the precipitation should be broadly forced. However, the latest mesoscale MDL trends have indicated some weak H7 frontogenetic signatures along with a moderate thermal gradient, with regions of instability possible above that layer. Verification of such would result in localized heavier snowfall totals. Latest trends have also suggested stronger lift in the dendritic growth layer as compared to previous MDL output which showed less dendritic UVM and snow ratios. PROGS indicate stronger QG convergence and ULVL PVA as a the left-exit region of a 120kt H5 speed max ejects from the base of an increasingly negatively-tilted trough. From 12 to 16Z, impressive isentropic lift is noted on the 280-285K SFCS, and a weak TROWAL feature is indicated on the 290K SFC, both of these features strongest between 50 mi S of I-80. Regarding snowfall totals, the Garcia method was investigated using the 285K SFC, this supports 12hr snowfall totals in excess of 5 inches between I-80 and US-30 in SERN IA, with lesser amounts to the N and S. Looking at NAM QPF, 0.3 inches is indicated, while the Cobb algorithm suggests 12:1 to 14:1 ratios.
Looking ahead… In the wake of Friday’s system, the ULVL pattern will transition towards an increasingly zonal flow as H85 WAA spreads into the upper-Midwest and return flow commences at the SFC.
- bill
[FONT="]8:55 PM CST, 12/27/07[/FONT]
