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_20260304_1800
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)
=== ===== === ==== ==== === === === ====
Wed 03/04 18Z 0.23 2809  75   1   0 0.00
Wed 03/04 19Z 0.28 2611  72   2   0 0.00
Wed 03/04 21Z 0.49 2617  61   7   0 0.00
Wed 03/04 22Z 0.50 2717  57  12   1 0.00
Wed 03/04 23Z 0.47 2716  56  17   1 0.00
Thu 03/05 00Z 0.44 2716  52  22   1 0.00
Thu 03/05 01Z 0.40 2715  48  25   2 0.00
Thu 03/05 02Z 0.39 2715  44  27   2 0.00
Thu 03/05 03Z 0.41 2716  44  28   2 0.00
Thu 03/05 05Z 0.37 2815  47  27   1 0.00
Thu 03/05 07Z 0.27 2812  52  16   1 0.00
Thu 03/05 08Z 0.24 2811  56  15   1 0.00
Thu 03/05 09Z 0.21 2809  60  15   1 0.00
Thu 03/05 10Z 0.18 2809  62  12   1 0.00
Thu 03/05 11Z 0.11 2906  64  11   1 0.00
Thu 03/05 12Z 0.05 3104  67  11   1 0.00
Thu 03/05 13Z 0.02 3302  69  11   1 0.00
Thu 03/05 14Z 0.03 1000  70  14   1 0.00
Thu 03/05 15Z 0.06 1104  71  15   1 0.00
Thu 03/05 16Z 0.08 1206  75  17   1 0.00
Thu 03/05 17Z 0.09 1308  77  18   0 0.00
Thu 03/05 18Z 0.10 1410  81  20   0 0.00
Thu 03/05 19Z 0.09 1412  84  22   0 0.00
Thu 03/05 20Z 0.09 1412  81  23   0 0.00
Thu 03/05 21Z 0.08 1412  76  24   0 0.00
Thu 03/05 22Z 0.08 1412  71  24   1 0.01
Thu 03/05 23Z 0.09 1412  70  25   1 0.01
Fri 03/06 00Z 0.11 1414  69  32   1 0.01
Fri 03/06 02Z 0.11 1417  75  53   1 0.01
Fri 03/06 03Z 0.12 1418  80  61   0 0.01
Fri 03/06 04Z 0.11 1417  85  69   0 0.01
Fri 03/06 05Z 0.11 1417  90  77   0 0.00
Fri 03/06 06Z 0.12 1419  93  88   0 0.00
Fri 03/06 07Z 0.10 1519  95  93   0 0.00
Fri 03/06 08Z 0.09 1518  96  97   0 0.00
Fri 03/06 09Z 0.08 1518  96  99   0 0.02
Fri 03/06 10Z 0.09 1518  95  97   0 0.03
Fri 03/06 11Z 0.10 1519  94  91   0 0.03
Fri 03/06 12Z 0.09 1519  95  85   0 0.03
Fri 03/06 13Z 0.10 1520  94  73   0 0.03
Fri 03/06 14Z 0.08 1520  94  66   0 0.02
Fri 03/06 15Z 0.08 1520  94  53   0 0.00
Fri 03/06 16Z 0.07 1519  94  49   0 0.00
Fri 03/06 18Z 0.03 1619  94  51   0 0.00
Fri 03/06 19Z 0.03 1718  95  58   0 0.00
Fri 03/06 20Z 0.03 1718  95  62   0 0.00
Fri 03/06 21Z 0.05 1721  94  55   0 0.00
Fri 03/06 22Z 0.07 1722  95  45   1 0.00
Fri 03/06 23Z 0.10 1823  96  40   1 0.00
Sat 03/07 00Z 0.13 1824  96  50   2 0.00
Sat 03/07 01Z 0.14 1825  97  39   2 0.00
Sat 03/07 02Z 0.16 1827  97  47   3 0.00
Sat 03/07 03Z 0.18 1929  97  39   3 0.00
Sat 03/07 04Z 0.19 1930  97  16   3 0.00
Sat 03/07 05Z 0.23 1930  97  29   3 0.01

Run total areal avg QPF for the Central_Greens is: 0.23 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