NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260228_0000
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)
=== ===== === ==== ==== === === === ====
Sat 02/28 00Z 1.04 2418  69  46  -6 0.00
Sat 02/28 01Z 0.89 2421  69  36  -5 0.00
Sat 02/28 02Z 0.78 2422  70  36  -4 0.00
Sat 02/28 03Z 0.76 2324  67  38  -4 0.00
Sat 02/28 04Z 0.76 2327  65  38  -3 0.00
Sat 02/28 05Z 0.71 2228  64  35  -2 0.00
Sat 02/28 06Z 0.65 2229  63  31  -2 0.00
Sat 02/28 07Z 0.64 2232  65  28  -2 0.00
Sat 02/28 08Z 0.66 2134  65  28  -2 0.00
Sat 02/28 09Z 0.66 2135  60  28  -1 0.00
Sat 02/28 10Z 0.61 2135  57  13  -1 0.00
Sat 02/28 11Z 0.58 2137  65  25  -1 0.00
Sat 02/28 12Z 0.54 2139  72  55  -1 0.00
Sat 02/28 13Z 0.55 2140  77  61   0 0.00
Sat 02/28 14Z 0.57 2142  76  73   0 0.00
Sat 02/28 15Z 0.69 2143  79  92   0 0.00
Sat 02/28 16Z 0.73 2142  84  95   0 0.00
Sat 02/28 17Z 0.80 2240  93  91  -1 0.03
Sat 02/28 18Z 0.80 2236  95  55  -1 0.01
Sat 02/28 19Z 0.95 2333  96  22  -2 0.01
Sat 02/28 20Z 1.21 2531  97  13  -3 0.01
Sat 02/28 21Z 1.26 2628  93   9  -4 0.01
Sat 02/28 22Z 1.05 2625  81   6  -4 0.01
Sat 02/28 23Z 0.81 2723  74   6  -5 0.01
Sun 03/01 00Z 0.62 2821  66   9  -6 0.01
Sun 03/01 01Z 0.50 2920  64  13  -6 0.00
Sun 03/01 02Z 0.43 2919  64  15  -7 0.01
Sun 03/01 03Z 0.38 3020  65  18  -7 0.01
Sun 03/01 04Z 0.29 3017  62  39  -7 0.00
Sun 03/01 05Z 0.23 3115  57  68  -7 0.00
Sun 03/01 06Z 0.20 3114  56  77  -8 0.00
Sun 03/01 07Z 0.19 3113  57  87  -9 0.00
Sun 03/01 08Z 0.19 3112  55  90 -10 0.00
Sun 03/01 09Z 0.20 3114  58  88 -11 0.00
Sun 03/01 10Z 0.18 3112  59  87 -11 0.00
Sun 03/01 11Z 0.16 3111  63  89 -12 0.00
Sun 03/01 12Z 0.15 3111  68  89 -13 0.00
Sun 03/01 13Z 0.17 3111  73  88 -13 0.00
Sun 03/01 14Z 0.15 3110  74  86 -14 0.00
Sun 03/01 15Z 0.16 3209  75  84 -14 0.00
Sun 03/01 16Z 0.24 3110  75  87 -15 0.00
Sun 03/01 17Z 0.30 3212  77  87 -16 0.00
Sun 03/01 18Z 0.36 3213  79  87 -17 0.00
Sun 03/01 19Z 0.35 3214  75  85 -17 0.00
Sun 03/01 20Z 0.43 3215  68  84 -17 0.00
Sun 03/01 21Z 0.45 3215  61  78 -17 0.00
Sun 03/01 22Z 0.34 3216  61  57 -17 0.00
Sun 03/01 23Z 0.34 3218  61  38 -18 0.00
Mon 03/02 00Z 0.38 3219  68  31 -18 0.00
Mon 03/02 01Z 0.43 3220  75  28 -19 0.00
Mon 03/02 02Z 0.51 3220  79  26 -20 0.00
Mon 03/02 03Z 0.55 3119  78  21 -20 0.00
Mon 03/02 04Z 0.52 3119  74  22 -21 0.00
Mon 03/02 05Z 0.46 3120  68  19 -21 0.00
Mon 03/02 06Z 0.42 3120  67  20 -21 0.00
Mon 03/02 07Z 0.38 3220  64  23 -21 0.00
Mon 03/02 08Z 0.36 3220  60  24 -21 0.00
Mon 03/02 09Z 0.33 3220  56  25 -21 0.00
Mon 03/02 10Z 0.32 3220  53  25 -21 0.00
Mon 03/02 11Z 0.31 3119  52  27 -21 0.00

Run total areal avg QPF for the greens is: 0.12 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