NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260216_0600
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)
=== ===== === ==== ==== === === === ====
Mon 02/16 06Z 0.06 1815  66  46  -6 0.00
Mon 02/16 07Z 0.08 1816  69  51  -6 0.00
Mon 02/16 08Z 0.07 1816  70  54  -6 0.00
Mon 02/16 09Z 0.07 1914  71  58  -5 0.00
Mon 02/16 10Z 0.07 1912  72  71  -5 0.00
Mon 02/16 11Z 0.07 1912  73  82  -5 0.00
Mon 02/16 12Z 0.05 1911  75  84  -4 0.00
Mon 02/16 13Z 0.04 1811  78  86  -4 0.00
Mon 02/16 16Z 0.08 2009  83  71  -4 0.00
Mon 02/16 17Z 0.06 1908  84  63  -4 0.00
Mon 02/16 18Z 0.05 1908  85  59  -4 0.00
Mon 02/16 19Z 0.03 1808  84  53  -4 0.00
Mon 02/16 22Z 0.05 1909  85  42  -4 0.00
Mon 02/16 23Z 0.06 1911  85  36  -3 0.00
Tue 02/17 00Z 0.09 1912  85  31  -3 0.00
Tue 02/17 01Z 0.15 2113  87  30  -2 0.00
Tue 02/17 02Z 0.18 2114  90  36  -2 0.00
Tue 02/17 03Z 0.20 2115  91  43  -2 0.00
Tue 02/17 04Z 0.25 2217  92  80  -3 0.00
Tue 02/17 05Z 0.27 2217  93  89  -3 0.00
Tue 02/17 06Z 0.28 2217  94  90  -3 0.00
Tue 02/17 07Z 0.26 2216  93  90  -3 0.00
Tue 02/17 08Z 0.27 2217  93  96  -3 0.00
Tue 02/17 09Z 0.26 2117  95  97  -3 0.00
Tue 02/17 10Z 0.25 2117  95  97  -3 0.01
Tue 02/17 11Z 0.23 2116  95  97  -2 0.01
Tue 02/17 12Z 0.27 2216  96  92  -3 0.00
Tue 02/17 13Z 0.27 2215  97  80  -3 0.01
Tue 02/17 14Z 0.30 2314  98  74  -3 0.01
Tue 02/17 15Z 0.32 2513  98  60  -3 0.01
Tue 02/17 16Z 0.34 2613  98  48  -3 0.01
Tue 02/17 17Z 0.31 2711  98  37  -3 0.01
Tue 02/17 18Z 0.31 2811  98  38  -3 0.01
Tue 02/17 19Z 0.37 2913  98  37  -3 0.02
Tue 02/17 20Z 0.38 2913  98  20  -3 0.01
Tue 02/17 21Z 0.42 2915  98  13  -3 0.01
Tue 02/17 22Z 0.44 2815  97  16  -4 0.01
Tue 02/17 23Z 0.51 2816  94  16  -4 0.00
Wed 02/18 00Z 0.52 2918  88  16  -3 0.00
Wed 02/18 01Z 0.45 2919  76  15  -3 0.01
Wed 02/18 02Z 0.43 2919  66  13  -3 0.01
Wed 02/18 03Z 0.44 2920  61  14  -3 0.01
Wed 02/18 04Z 0.44 2920  58  18  -3 0.01
Wed 02/18 05Z 0.45 2921  57  17  -4 0.01
Wed 02/18 06Z 0.46 2921  56  16  -4 0.01
Wed 02/18 07Z 0.42 3021  54  14  -4 0.01
Wed 02/18 08Z 0.38 3020  52  15  -4 0.01
Wed 02/18 09Z 0.31 3019  49  21  -4 0.01
Wed 02/18 10Z 0.30 3018  46  34  -3 0.01
Wed 02/18 11Z 0.26 3016  42  38  -3 0.01
Wed 02/18 12Z 0.22 2913  41  44  -3 0.01
Wed 02/18 13Z 0.20 2911  40  60  -3 0.01
Wed 02/18 14Z 0.16 2808  40  65  -3 0.00
Wed 02/18 15Z 0.13 2606  47  67  -3 0.00
Wed 02/18 16Z 0.12 2506  57  80  -3 0.00
Wed 02/18 17Z 0.10 2405  68  84  -3 0.00

Run total areal avg QPF for the greens is: 0.26 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