NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260111_1200
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 01/11 12Z 0.38 2411  99  25  -4 0.00
Sun 01/11 13Z 0.47 2513  98  19  -4 0.01
Sun 01/11 14Z 0.70 2618  96  29  -5 0.01
Sun 01/11 15Z 0.70 2719  96  26  -5 0.01
Sun 01/11 16Z 0.57 2717  91  51  -5 0.00
Sun 01/11 17Z 0.52 2716  84  61  -5 0.00
Sun 01/11 18Z 0.69 2717  88  60  -7 0.00
Sun 01/11 19Z 0.78 2716  91  66  -7 0.00
Sun 01/11 20Z 0.88 2715  90  75  -8 0.00
Sun 01/11 21Z 1.06 2717  90  79  -8 0.00
Sun 01/11 22Z 1.38 2620  90  64  -9 0.00
Sun 01/11 23Z 2.03 2723  88  52  -9 0.00
Mon 01/12 00Z 1.42 2722  86  77  -9 0.00
Mon 01/12 01Z 1.28 2622  93  84  -9 0.00
Mon 01/12 02Z 1.28 2724  94  80 -10 0.02
Mon 01/12 03Z 1.51 2827  95  81 -11 0.03
Mon 01/12 04Z 2.42 2930  91  80 -13 0.03
Mon 01/12 05Z 2.76 2931  88  80 -15 0.01
Mon 01/12 06Z 2.47 2932  90  69 -16 0.01
Mon 01/12 07Z 1.70 2932  92  45 -16 0.00
Mon 01/12 08Z 1.06 2933  91  42 -15 0.00
Mon 01/12 09Z 0.67 3034  88  53 -13 0.00
Mon 01/12 10Z 0.57 3035  87  11 -11 0.00
Mon 01/12 11Z 0.56 3035  78   9 -11 0.00
Mon 01/12 12Z 0.51 3034  62   9 -10 0.00
Mon 01/12 13Z 0.56 2933  69  20 -10 0.00
Mon 01/12 14Z 0.60 2935  65  27 -10 0.00
Mon 01/12 15Z 0.60 2933  68  44 -10 0.00
Mon 01/12 16Z 0.65 2831  76  71 -10 0.00
Mon 01/12 17Z 0.74 2830  80  75 -10 0.00
Mon 01/12 18Z 0.75 2727  84  77  -9 0.00
Mon 01/12 19Z 0.76 2626  88  74  -9 0.00
Mon 01/12 20Z 0.80 2628  91  76  -9 0.00
Mon 01/12 21Z 0.95 2628  94  83  -9 0.00
Mon 01/12 22Z 1.12 2529  95  85 -10 0.00
Mon 01/12 23Z 1.29 2630  94  86 -10 0.01
Tue 01/13 00Z 1.43 2528  94  81 -10 0.00
Tue 01/13 01Z 1.54 2628  95  79 -10 0.00
Tue 01/13 02Z 1.46 2629  95  75 -10 0.00
Tue 01/13 03Z 1.30 2629  96  66 -10 0.00
Tue 01/13 04Z 1.07 2628  95  54  -9 0.00
Tue 01/13 05Z 0.91 2626  95  70  -9 0.00
Tue 01/13 06Z 0.87 2626  95  64  -9 0.00
Tue 01/13 07Z 0.88 2726  95  50  -9 0.01
Tue 01/13 08Z 0.87 2725  95  46  -9 0.01
Tue 01/13 09Z 0.84 2725  95  49  -9 0.01
Tue 01/13 10Z 0.77 2724  95  48  -8 0.01
Tue 01/13 11Z 0.73 2725  94  39  -8 0.01
Tue 01/13 12Z 0.63 2723  92  27  -6 0.01
Tue 01/13 13Z 0.55 2623  90  19  -5 0.01
Tue 01/13 14Z 0.47 2621  84  12  -4 0.01
Tue 01/13 15Z 0.40 2520  79  12  -3 0.00
Tue 01/13 16Z 0.37 2519  76  15  -2 0.00
Tue 01/13 17Z 0.35 2419  71  16  -1 0.00
Tue 01/13 18Z 0.36 2420  67  17   0 0.00
Tue 01/13 19Z 0.37 2421  65  29   0 0.00
Tue 01/13 20Z 0.38 2422  71  67   0 0.00
Tue 01/13 21Z 0.42 2423  73  66   0 0.00
Tue 01/13 22Z 0.43 2324  71  82   0 0.00
Tue 01/13 23Z 0.43 2225  64  75   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.22 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