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