NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261029_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)
=== ===== === ==== ==== === === === ====
Thu 10/29 12Z 0.46 2516  76  34   7 0.00
Thu 10/29 13Z 0.47 2517  76  36   7 0.00
Thu 10/29 14Z 0.48 2518  76  37   7 0.00
Thu 10/29 15Z 0.49 2419  76  39   7 0.00
Thu 10/29 16Z 0.55 2421  76  53   7 0.00
Thu 10/29 17Z 0.64 2424  75  59   8 0.00
Thu 10/29 18Z 0.74 2425  70  56   8 0.00
Thu 10/29 19Z 0.82 2426  67  52   8 0.00
Thu 10/29 20Z 0.80 2426  67  40   9 0.00
Thu 10/29 21Z 0.79 2527  67  35   9 0.00
Thu 10/29 22Z 0.82 2429  68  70   9 0.00
Thu 10/29 23Z 0.83 2431  72  87   9 0.00
Fri 10/30 00Z 0.84 2531  75  88   9 0.00
Fri 10/30 01Z 0.87 2533  75  89   9 0.00
Fri 10/30 02Z 0.97 2534  81  94   9 0.02
Fri 10/30 03Z 0.97 2533  83  93   9 0.02
Fri 10/30 04Z 1.00 2534  86  93   8 0.03
Fri 10/30 05Z 0.96 2633  92  94   8 0.04
Fri 10/30 06Z 0.86 2632  95  88   8 0.05
Fri 10/30 07Z 0.78 2729  96  90   8 0.03
Fri 10/30 08Z 0.71 2726  96  73   7 0.03
Fri 10/30 09Z 0.75 2726  96  37   7 0.02
Fri 10/30 10Z 0.81 2727  94  13   6 0.01
Fri 10/30 11Z 0.81 2827  83   8   6 0.01
Fri 10/30 12Z 0.82 2827  80  10   5 0.01
Fri 10/30 13Z 0.77 2826  79   9   4 0.01
Fri 10/30 14Z 0.74 2825  82   4   3 0.01
Fri 10/30 15Z 0.73 2824  84   3   2 0.01
Fri 10/30 16Z 0.80 2924  89   9   1 0.01
Fri 10/30 17Z 0.99 2924  89  10   0 0.01
Fri 10/30 18Z 1.06 2924  89  11   0 0.00
Fri 10/30 19Z 1.23 2926  90  12   0 0.00
Fri 10/30 20Z 1.39 3027  93  16  -1 0.01
Fri 10/30 21Z 1.16 3028  94  13  -2 0.01
Fri 10/30 22Z 0.92 3029  94   7  -2 0.00
Fri 10/30 23Z 0.83 3130  94  12  -2 0.00
Sat 10/31 00Z 0.82 3130  96  17  -2 0.00
Sat 10/31 01Z 0.82 3131  97  19  -3 0.01
Sat 10/31 02Z 0.80 3132  96  23  -3 0.01
Sat 10/31 03Z 0.71 3132  97  26  -3 0.01
Sat 10/31 04Z 0.62 3231  94  28  -4 0.01
Sat 10/31 05Z 0.48 3230  91  29  -5 0.01
Sat 10/31 06Z 0.40 3230  87  19  -5 0.00
Sat 10/31 07Z 0.33 3329  87   9  -5 0.00
Sat 10/31 08Z 0.35 3329  91   6  -6 0.00
Sat 10/31 09Z 0.28 3325  91   8  -6 0.00
Sat 10/31 10Z 0.24 3222  88   8  -5 0.00
Sat 10/31 11Z 0.23 3222  82  19  -5 0.00
Sat 10/31 12Z 0.23 3222  74  22  -4 0.00
Sat 10/31 13Z 0.20 3221  66  20  -3 0.00
Sat 10/31 14Z 0.18 3220  57  21  -2 0.00
Sat 10/31 15Z 0.18 3219  49  24  -2 0.00
Sat 10/31 16Z 0.17 3217  42  20  -2 0.00
Sat 10/31 17Z 0.18 3216  38  19  -2 0.00
Sat 10/31 18Z 0.17 3216  35  18  -1 0.00
Sat 10/31 19Z 0.16 3215  34  20   0 0.00
Sat 10/31 20Z 0.19 3114  39  29  -1 0.00
Sat 10/31 21Z 0.23 3012  46  30  -1 0.00
Sat 10/31 22Z 0.28 2913  51  25  -1 0.00
Sat 10/31 23Z 0.30 2913  51  25   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.39 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