Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260307_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 03/07 00Z 0.08 1918  94  17   0 0.00
Sat 03/07 01Z 0.11 1921  94  22   0 0.00
Sat 03/07 02Z 0.14 1923  94  36   1 0.00
Sat 03/07 03Z 0.15 1925  95  48   1 0.00
Sat 03/07 04Z 0.18 2027  95  48   2 0.00
Sat 03/07 05Z 0.18 2027  94  35   3 0.01
Sat 03/07 06Z 0.24 2128  95  26   4 0.01
Sat 03/07 07Z 0.28 2128  95  25   5 0.01
Sat 03/07 08Z 0.25 2127  93  72   6 0.01
Sat 03/07 09Z 0.25 2130  94  95   7 0.01
Sat 03/07 10Z 0.28 2134  95  95   8 0.02
Sat 03/07 11Z 0.34 2135  96  85   9 0.04
Sat 03/07 12Z 0.37 2235  95  71   9 0.01
Sat 03/07 13Z 0.44 2237  96  84   9 0.06
Sat 03/07 14Z 0.50 2338  97  91   9 0.06
Sat 03/07 15Z 0.52 2436  96  91   9 0.07
Sat 03/07 16Z 0.51 2434  95  85  10 0.04
Sat 03/07 17Z 0.50 2434  92  83  10 0.01
Sat 03/07 18Z 0.61 2439  96  92  10 0.01
Sat 03/07 19Z 0.60 2436  89  84  11 0.06
Sat 03/07 20Z 0.59 2337  90  71  11 0.00
Sat 03/07 21Z 0.62 2340  91  62  11 0.00
Sat 03/07 22Z 0.63 2340  87  41  11 0.00
Sat 03/07 23Z 0.65 2340  86  43  12 0.00
Sun 03/08 00Z 0.68 2341  87  59  11 0.00
Sun 03/08 01Z 0.65 2340  87  72  11 0.00
Sun 03/08 02Z 0.65 2341  90  95  11 0.03
Sun 03/08 03Z 0.75 2344  95  96  11 0.16
Sun 03/08 04Z 0.76 2441  96  94  10 0.15
Sun 03/08 05Z 0.80 2440  95  82   9 0.17
Sun 03/08 06Z 0.74 2535  95  92   9 0.05
Sun 03/08 07Z 0.74 2534  95  89   9 0.03
Sun 03/08 08Z 0.76 2533  96  81   8 0.06
Sun 03/08 09Z 0.76 2532  94  57   8 0.04
Sun 03/08 10Z 0.81 2533  95  29   7 0.02
Sun 03/08 11Z 0.96 2534  96  24   6 0.02
Sun 03/08 12Z 1.12 2535  94  16   4 0.02
Sun 03/08 13Z 1.33 2538  94  17   3 0.02
Sun 03/08 15Z 1.22 2732  94   4   0 0.03
Sun 03/08 16Z 1.28 2730  94   3  -1 0.02
Sun 03/08 17Z 1.20 2728  95   3  -2 0.02
Sun 03/08 18Z 1.25 2725  95   3  -3 0.01
Sun 03/08 19Z 1.09 2624  94   4  -3 0.01
Sun 03/08 20Z 1.03 2626  93   5  -3 0.01
Sun 03/08 21Z 0.90 2627  88  11  -2 0.01
Sun 03/08 22Z 0.75 2629  77  23  -1 0.01
Sun 03/08 23Z 0.70 2631  66  81   0 0.00
Mon 03/09 00Z 0.71 2633  59  60   0 0.00
Mon 03/09 01Z 0.79 2636  60  30   0 0.00
Mon 03/09 02Z 0.93 2639  62  12   0 0.00
Mon 03/09 03Z 1.04 2640  73  18  -1 0.00
Mon 03/09 04Z 0.98 2638  75  29   0 0.00
Mon 03/09 05Z 0.89 2736  73  33   0 0.00
Mon 03/09 06Z 0.83 2635  70  42   0 0.00
Mon 03/09 07Z 0.81 2634  69  45   1 0.00
Mon 03/09 08Z 0.74 2632  65  52   2 0.00
Mon 03/09 09Z 0.78 2634  66  59   2 0.00
Mon 03/09 10Z 0.75 2535  62  72   3 0.00
Mon 03/09 11Z 0.72 2535  58  84   4 0.00

Run total areal avg QPF for the greens is: 1.32 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