National Weather Service United States Department of Commerce

A wintry mix is expected late Thursday into Friday Morning for southern Vermont and portions of northern New York.

A wintry mix of snow, sleet, and freezing rain will spread northward late Thursday through Friday Morning, mainly in southern Vermont and portions of northern New York. Precipitation will likely start as snow for most before transiting to a wintry mix Thursday night. Total snow and sleet accumulations up to one inch and ice accumulations up to two tenths of an inch are expected. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260305_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 03/05 06Z 0.24 2710  52  20   2 0.00
Thu 03/05 07Z 0.26 2711  49  16   1 0.00
Thu 03/05 08Z 0.24 2710  49  14   1 0.00
Thu 03/05 09Z 0.23 2710  47  13   1 0.00
Thu 03/05 10Z 0.17 2808  48  14   1 0.00
Thu 03/05 11Z 0.09 3005  50  15   1 0.00
Thu 03/05 12Z 0.03 3203  51  17   1 0.00
Thu 03/05 13Z 0.03 0000  54  19   2 0.00
Thu 03/05 14Z 0.05 1203  56  21   1 0.00
Thu 03/05 15Z 0.09 1207  64  23   1 0.00
Thu 03/05 16Z 0.10 1309  69  22   1 0.00
Thu 03/05 17Z 0.08 1410  75  22   0 0.00
Thu 03/05 18Z 0.11 1412  80  21   0 0.00
Thu 03/05 19Z 0.11 1412  85  20   0 0.00
Thu 03/05 20Z 0.10 1412  84  19   0 0.01
Thu 03/05 21Z 0.09 1412  82  20   0 0.01
Thu 03/05 22Z 0.10 1413  79  21   0 0.00
Thu 03/05 23Z 0.10 1414  80  25   0 0.00
Fri 03/06 00Z 0.13 1316  79  35   0 0.00
Fri 03/06 01Z 0.14 1317  82  43   0 0.00
Fri 03/06 02Z 0.14 1418  85  56   0 0.00
Fri 03/06 03Z 0.15 1318  86  65   0 0.01
Fri 03/06 04Z 0.15 1419  90  72   0 0.01
Fri 03/06 05Z 0.16 1421  92  75   0 0.01
Fri 03/06 06Z 0.17 1422  94  77   0 0.02
Fri 03/06 07Z 0.18 1323  95  79   0 0.02
Fri 03/06 08Z 0.17 1422  95  80   0 0.04
Fri 03/06 09Z 0.16 1422  95  81   0 0.04
Fri 03/06 10Z 0.14 1421  95  82   0 0.04
Fri 03/06 11Z 0.13 1420  95  81   0 0.04
Fri 03/06 12Z 0.15 1419  95  72   0 0.02
Fri 03/06 13Z 0.12 1418  95  63  -1 0.00
Fri 03/06 14Z 0.12 1419  94  53  -1 0.00
Fri 03/06 15Z 0.10 1518  94  45  -1 0.00
Fri 03/06 16Z 0.07 1518  94  41  -1 0.00
Fri 03/06 17Z 0.06 1617  95  35  -1 0.00
Fri 03/06 18Z 0.05 1616  95  34  -1 0.00
Fri 03/06 19Z 0.04 1618  94  33  -1 0.00
Fri 03/06 20Z 0.04 1619  92  43   0 0.00
Fri 03/06 21Z 0.04 1620  92  47   0 0.00
Fri 03/06 22Z 0.07 1721  94  51   0 0.00
Fri 03/06 23Z 0.10 1822  93  54   0 0.00
Sat 03/07 00Z 0.10 1823  91  55   0 0.00
Sat 03/07 01Z 0.12 1825  91  52   1 0.00
Sat 03/07 02Z 0.16 1826  93  44   1 0.00
Sat 03/07 03Z 0.18 1926  93  41   2 0.00
Sat 03/07 04Z 0.20 1924  94  45   3 0.00
Sat 03/07 05Z 0.19 1922  95  29   4 0.01
Sat 03/07 07Z 0.24 2023  96  76   4 0.01
Sat 03/07 08Z 0.26 2123  95  95   5 0.01
Sat 03/07 09Z 0.29 2124  96  71   5 0.01
Sat 03/07 10Z 0.29 2125  96  92   6 0.01
Sat 03/07 11Z 0.35 2128  97  95   7 0.01
Sat 03/07 12Z 0.39 2229  97  96   8 0.01
Sat 03/07 13Z 0.43 2229  97  85   8 0.02
Sat 03/07 14Z 0.45 2330  94  46   9 0.02
Sat 03/07 15Z 0.49 2332  96  33  10 0.01
Sat 03/07 16Z 0.54 2334  96  35  10 0.01
Sat 03/07 17Z 0.54 2334  93  37  10 0.02

Run total areal avg QPF for the Central_Greens is: 0.42 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1