NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260307_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)
=== ===== === ==== ==== === === === ====
Sat 03/07 12Z 0.36 2131  82  79   8 0.00
Sat 03/07 13Z 0.42 2233  88  87   9 0.00
Sat 03/07 14Z 0.48 2335  93  86   9 0.02
Sat 03/07 15Z 0.50 2434  93  65  10 0.00
Sat 03/07 16Z 0.47 2431  89  76  11 0.00
Sat 03/07 17Z 0.48 2430  90  78  11 0.01
Sat 03/07 18Z 0.49 2331  86  73  12 0.00
Sat 03/07 19Z 0.52 2333  88  73  12 0.00
Sat 03/07 20Z 0.59 2336  88  84  12 0.00
Sat 03/07 21Z 0.64 2338  88  83  12 0.00
Sat 03/07 22Z 0.71 2342  87  67  12 0.00
Sat 03/07 23Z 0.71 2343  85  47  13 0.00
Sun 03/08 00Z 0.76 2347  85  77  13 0.00
Sun 03/08 01Z 0.85 2349  87  88  12 0.00
Sun 03/08 02Z 0.83 2445  90  82  11 0.00
Sun 03/08 03Z 0.76 2441  96  80  11 0.01
Sun 03/08 04Z 0.74 2440  97  81  10 0.02
Sun 03/08 05Z 0.75 2441  98  85  10 0.03
Sun 03/08 06Z 0.78 2442  97  93  11 0.07
Sun 03/08 07Z 0.77 2537  97  92   9 0.15
Sun 03/08 08Z 0.74 2634  91  88   8 0.07
Sun 03/08 09Z 0.79 2634  93  60   7 0.04
Sun 03/08 10Z 0.90 2637  92  30   7 0.01
Sun 03/08 11Z 1.11 2637  92  32   5 0.01
Sun 03/08 12Z 1.06 2636  87   9   4 0.01
Sun 03/08 13Z 1.05 2635  89  10   3 0.02
Sun 03/08 14Z 0.99 2633  89   8   2 0.01
Sun 03/08 15Z 0.94 2631  90   6   1 0.01
Sun 03/08 16Z 0.88 2629  89   4   1 0.01
Sun 03/08 17Z 0.85 2626  90   5   0 0.01
Sun 03/08 18Z 0.82 2623  89   7   0 0.01
Sun 03/08 19Z 0.78 2623  86   6   0 0.00
Sun 03/08 20Z 0.84 2625  84   8   0 0.00
Sun 03/08 21Z 0.87 2627  83  14   0 0.00
Sun 03/08 22Z 0.81 2629  80  21   0 0.00
Sun 03/08 23Z 0.75 2631  76  65   0 0.00
Mon 03/09 00Z 0.73 2633  66  73   0 0.01
Mon 03/09 01Z 0.87 2639  68  41   0 0.01
Mon 03/09 02Z 1.18 2640  82  22  -2 0.01
Mon 03/09 03Z 1.48 2639  92   9  -2 0.00
Mon 03/09 04Z 1.33 2737  92   6  -2 0.00
Mon 03/09 05Z 1.12 2737  89  11  -1 0.00
Mon 03/09 07Z 0.88 2736  70  25   0 0.00
Mon 03/09 08Z 0.78 2735  61  31   1 0.00
Mon 03/09 09Z 0.72 2733  55  44   1 0.00
Mon 03/09 10Z 0.67 2732  49  61   2 0.00
Mon 03/09 11Z 0.69 2632  50  81   3 0.00
Mon 03/09 12Z 0.65 2631  56  74   3 0.00
Mon 03/09 13Z 0.65 2532  61  61   4 0.00
Mon 03/09 14Z 0.68 2434  60  43   5 0.00
Mon 03/09 15Z 0.73 2438  42  42   6 0.00
Mon 03/09 16Z 0.79 2438  50  60   7 0.00
Mon 03/09 17Z 0.87 2438  49  56   7 0.00
Mon 03/09 18Z 0.87 2436  52  63   7 0.00
Mon 03/09 19Z 0.90 2435  54  63   7 0.00
Mon 03/09 20Z 0.98 2435  57  57   7 0.00
Mon 03/09 21Z 1.07 2436  60  48   7 0.00
Mon 03/09 22Z 1.15 2437  60  40   7 0.00
Mon 03/09 23Z 1.20 2538  55  31   7 0.00

Run total areal avg QPF for the Central_Greens is: 0.55 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