NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260215_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)
=== ===== === ==== ==== === === === ====
Sun 02/15 06Z 0.58 2923  81  21  -9 0.00
Sun 02/15 07Z 0.57 3025  85  24  -9 0.00
Sun 02/15 08Z 0.48 3024  89  25  -9 0.00
Sun 02/15 09Z 0.37 3123  93  26  -9 0.00
Sun 02/15 10Z 0.24 3121  91  27  -9 0.00
Sun 02/15 11Z 0.16 3219  85  27  -9 0.00
Sun 02/15 12Z 0.11 3317  72  24  -8 0.00
Sun 02/15 13Z 0.07 3316  58  22  -8 0.00
Sun 02/15 14Z 0.03 3413  46  22  -8 0.00
Sun 02/15 15Z 0.03 3510  38  24  -7 0.00
Sun 02/15 16Z 0.06 0107  35  29  -7 0.00
Sun 02/15 17Z 0.07 0304  33  33  -7 0.00
Sun 02/15 19Z 0.06 1203  35  47  -7 0.00
Sun 02/15 20Z 0.02 1604  36  51  -7 0.00
Sun 02/15 21Z 0.01 1704  33  49  -5 0.00
Sun 02/15 22Z 0.02 1605  29  37  -4 0.00
Sun 02/15 23Z 0.02 1708  31  25  -5 0.00
Mon 02/16 00Z 0.02 1710  33  20  -4 0.00
Mon 02/16 01Z 0.03 1710  37  24  -4 0.00
Mon 02/16 02Z 0.04 1711  45  38  -4 0.00
Mon 02/16 03Z 0.06 1812  53  47  -5 0.00
Mon 02/16 04Z 0.10 1913  64  48  -5 0.00
Mon 02/16 05Z 0.12 1913  77  47  -6 0.00
Mon 02/16 06Z 0.13 1914  87  50  -6 0.00
Mon 02/16 07Z 0.11 1913  91  58  -5 0.00
Mon 02/16 08Z 0.10 1912  90  74  -5 0.00
Mon 02/16 09Z 0.09 1911  91  88  -4 0.00
Mon 02/16 10Z 0.10 1911  92  94  -5 0.00
Mon 02/16 11Z 0.10 1911  92  97  -5 0.00
Mon 02/16 12Z 0.08 1911  92  89  -5 0.01
Mon 02/16 13Z 0.10 1912  93  82  -5 0.01
Mon 02/16 14Z 0.11 2011  94  72  -4 0.00
Mon 02/16 15Z 0.14 2011  94  65  -4 0.00
Mon 02/16 16Z 0.15 2110  95  55  -4 0.00
Mon 02/16 17Z 0.16 2110  95  44  -4 0.00
Mon 02/16 18Z 0.14 2009  95  32  -4 0.00
Mon 02/16 19Z 0.16 2110  95  25  -4 0.00
Mon 02/16 20Z 0.19 2111  95  25  -4 0.00
Mon 02/16 21Z 0.25 2212  94  33  -4 0.00
Mon 02/16 22Z 0.23 2212  93  50  -3 0.00
Mon 02/16 23Z 0.29 2214  94  57  -4 0.00
Tue 02/17 00Z 0.34 2216  94  89  -4 0.00
Tue 02/17 01Z 0.36 2317  92  90  -3 0.00
Tue 02/17 02Z 0.40 2317  90  92  -3 0.00
Tue 02/17 03Z 0.44 2418  95  93  -4 0.01
Tue 02/17 04Z 0.46 2420  97  91  -3 0.02
Tue 02/17 05Z 0.44 2418  96  91  -3 0.03
Tue 02/17 06Z 0.46 2419  97  91  -3 0.03
Tue 02/17 07Z 0.45 2419  94  89  -2 0.03
Tue 02/17 08Z 0.43 2418  95  86  -2 0.02
Tue 02/17 09Z 0.39 2516  94  75  -2 0.02
Tue 02/17 10Z 0.34 2514  95  65  -2 0.01
Tue 02/17 11Z 0.31 2613  96  47  -2 0.01
Tue 02/17 12Z 0.28 2712  97  35  -2 0.01
Tue 02/17 13Z 0.28 2812  97  27  -3 0.01
Tue 02/17 14Z 0.25 2911  97  21  -3 0.01
Tue 02/17 15Z 0.21 3010  96  14  -3 0.01
Tue 02/17 16Z 0.21 3009  96   7  -3 0.01
Tue 02/17 17Z 0.22 3009  95   9  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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