Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260307_0000
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)
=== ===== === ==== ==== === === === ====
Sat 03/07 00Z 0.12 1918  96  20   0 0.00
Sat 03/07 01Z 0.17 1920  96  18   0 0.00
Sat 03/07 02Z 0.20 1922  96  34   1 0.00
Sat 03/07 03Z 0.21 1924  96  45   1 0.01
Sat 03/07 04Z 0.23 1925  97  45   2 0.01
Sat 03/07 05Z 0.23 2025  96  29   3 0.01
Sat 03/07 06Z 0.29 2126  97  20   4 0.01
Sat 03/07 07Z 0.32 2126  96  23   5 0.01
Sat 03/07 08Z 0.30 2126  96  69   6 0.01
Sat 03/07 09Z 0.30 2128  96  94   7 0.01
Sat 03/07 10Z 0.32 2132  97  95   7 0.01
Sat 03/07 11Z 0.37 2132  97  85   8 0.04
Sat 03/07 12Z 0.39 2232  96  64   9 0.01
Sat 03/07 13Z 0.46 2235  95  78   9 0.03
Sat 03/07 14Z 0.53 2337  96  91   9 0.04
Sat 03/07 15Z 0.55 2436  95  90   9 0.07
Sat 03/07 16Z 0.54 2434  94  86  10 0.04
Sat 03/07 17Z 0.54 2434  93  86  10 0.01
Sat 03/07 18Z 0.64 2438  97  94  10 0.02
Sat 03/07 19Z 0.63 2436  90  87  11 0.07
Sat 03/07 20Z 0.61 2336  92  70  11 0.00
Sat 03/07 21Z 0.63 2337  90  70  11 0.00
Sat 03/07 22Z 0.64 2338  86  52  12 0.00
Sat 03/07 23Z 0.65 2338  85  36  12 0.00
Sun 03/08 00Z 0.66 2339  86  45  12 0.01
Sun 03/08 01Z 0.64 2338  87  60  12 0.01
Sun 03/08 02Z 0.66 2341  89  95  12 0.02
Sun 03/08 03Z 0.74 2345  95  95  11 0.12
Sun 03/08 04Z 0.74 2342  97  96  10 0.20
Sun 03/08 05Z 0.79 2540  97  94   9 0.26
Sun 03/08 06Z 0.72 2435  96  93   9 0.07
Sun 03/08 07Z 0.74 2535  95  86   9 0.03
Sun 03/08 08Z 0.75 2534  97  79   8 0.06
Sun 03/08 09Z 0.75 2533  96  60   8 0.05
Sun 03/08 10Z 0.79 2534  94  32   7 0.02
Sun 03/08 11Z 0.93 2536  96  16   6 0.02
Sun 03/08 12Z 1.11 2537  93  14   5 0.02
Sun 03/08 13Z 1.23 2538  92  13   3 0.02
Sun 03/08 15Z 1.23 2631  93   4   0 0.02
Sun 03/08 16Z 1.25 2730  91   4   0 0.01
Sun 03/08 17Z 1.22 2728  93   3  -1 0.01
Sun 03/08 18Z 1.29 2625  94   3  -2 0.01
Sun 03/08 19Z 1.08 2624  93   3  -2 0.00
Sun 03/08 20Z 0.99 2626  91   3  -2 0.00
Sun 03/08 21Z 0.88 2627  86   9  -2 0.01
Sun 03/08 22Z 0.73 2629  75  22  -1 0.01
Sun 03/08 23Z 0.69 2631  67  77   0 0.00
Mon 03/09 00Z 0.70 2633  59  50   0 0.00
Mon 03/09 01Z 0.77 2637  56  21   0 0.00
Mon 03/09 02Z 0.91 2640  59   9   0 0.00
Mon 03/09 03Z 1.06 2641  70  18   0 0.00
Mon 03/09 04Z 0.99 2639  72  26   0 0.00
Mon 03/09 05Z 0.88 2737  71  27   0 0.00
Mon 03/09 06Z 0.80 2635  67  32   1 0.00
Mon 03/09 07Z 0.76 2634  66  39   1 0.00
Mon 03/09 08Z 0.69 2632  64  46   2 0.00
Mon 03/09 09Z 0.73 2633  65  56   2 0.00
Mon 03/09 10Z 0.71 2534  60  68   3 0.00
Mon 03/09 11Z 0.69 2534  57  79   4 0.00

Run total areal avg QPF for the Central_Greens is: 1.39 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