NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260215_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 02/15 12Z 0.14 3315  73   9 -11 0.00
Sun 02/15 13Z 0.10 3415  57  11 -11 0.00
Sun 02/15 14Z 0.08 3513  43  12 -10 0.00
Sun 02/15 15Z 0.09 0111  35  14  -9 0.00
Sun 02/15 16Z 0.13 0310  33  18  -8 0.00
Sun 02/15 17Z 0.14 0508  31  23  -8 0.00
Sun 02/15 18Z 0.14 0806  31  30  -7 0.00
Sun 02/15 19Z 0.12 1005  31  38  -7 0.00
Sun 02/15 20Z 0.10 1205  30  44  -6 0.00
Sun 02/15 21Z 0.09 1306  28  45  -6 0.00
Sun 02/15 22Z 0.08 1507  26  41  -5 0.00
Sun 02/15 23Z 0.06 1609  25  36  -5 0.00
Mon 02/16 00Z 0.06 1611  25  36  -5 0.00
Mon 02/16 01Z 0.04 1712  30  37  -5 0.00
Mon 02/16 02Z 0.02 1713  36  36  -5 0.00
Mon 02/16 03Z 0.02 1814  44  36  -5 0.00
Mon 02/16 04Z 0.03 1814  53  41  -6 0.00
Mon 02/16 05Z 0.05 1815  62  50  -6 0.00
Mon 02/16 06Z 0.05 1815  70  68  -6 0.00
Mon 02/16 07Z 0.04 1816  73  84  -6 0.00
Mon 02/16 08Z 0.04 1816  76  89  -5 0.00
Mon 02/16 09Z 0.03 1814  81  90  -5 0.01
Mon 02/16 10Z 0.04 1814  84  92  -5 0.00
Mon 02/16 11Z 0.06 1914  85  89  -6 0.00
Mon 02/16 12Z 0.08 1914  88  91  -5 0.00
Mon 02/16 13Z 0.08 1913  89  83  -5 0.00
Mon 02/16 14Z 0.08 1913  90  73  -4 0.00
Mon 02/16 15Z 0.10 2013  91  61  -4 0.00
Mon 02/16 16Z 0.10 2011  92  54  -4 0.00
Mon 02/16 17Z 0.08 2010  92  46  -4 0.00
Mon 02/16 18Z 0.09 2010  92  40  -4 0.00
Mon 02/16 19Z 0.12 2011  91  36  -4 0.00
Mon 02/16 20Z 0.15 2112  91  35  -4 0.00
Mon 02/16 21Z 0.15 2012  91  39  -4 0.00
Mon 02/16 22Z 0.15 2013  90  38  -3 0.00
Mon 02/16 23Z 0.19 2115  92  34  -4 0.00
Tue 02/17 00Z 0.24 2116  93  48  -4 0.00
Tue 02/17 01Z 0.29 2218  93  86  -4 0.00
Tue 02/17 02Z 0.37 2220  94  90  -4 0.00
Tue 02/17 03Z 0.34 2318  88  90  -3 0.00
Tue 02/17 04Z 0.32 2416  87  91  -3 0.00
Tue 02/17 05Z 0.30 2415  85  94  -3 0.00
Tue 02/17 06Z 0.35 2417  87  92  -3 0.00
Tue 02/17 07Z 0.33 2415  90  92  -3 0.00
Tue 02/17 08Z 0.33 2415  94  94  -3 0.00
Tue 02/17 09Z 0.33 2415  94  91  -2 0.01
Tue 02/17 10Z 0.35 2514  91  92  -3 0.01
Tue 02/17 11Z 0.36 2514  91  87  -3 0.01
Tue 02/17 12Z 0.36 2613  93  74  -3 0.01
Tue 02/17 13Z 0.37 2614  95  62  -3 0.01
Tue 02/17 14Z 0.35 2713  96  50  -3 0.01
Tue 02/17 15Z 0.30 2711  96  37  -3 0.01
Tue 02/17 16Z 0.28 2810  96  19  -3 0.00
Tue 02/17 17Z 0.30 2811  96  13  -3 0.00
Tue 02/17 18Z 0.31 2811  95  22  -3 0.00
Tue 02/17 19Z 0.35 2812  95  23  -3 0.00
Tue 02/17 20Z 0.37 2913  92  24  -3 0.00
Tue 02/17 21Z 0.37 2813  88  24  -3 0.00
Tue 02/17 22Z 0.39 2814  81  22  -3 0.00
Tue 02/17 23Z 0.38 2814  72  19  -3 0.01

Run total areal avg QPF for the greens is: 0.09 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