NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260508_1800
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)
=== ===== === ==== ==== === === === ====
Fri 05/08 18Z 4.95 2807  65  80  -2 0.00
Fri 05/08 19Z 6.02 2608  63  86  -1 0.00
Fri 05/08 20Z 5.24 2608  68  90  -1 0.00
Fri 05/08 21Z 3.38 2610  76  87  -1 0.00
Fri 05/08 22Z 1.66 2610  76  74  -1 0.00
Fri 05/08 23Z 0.83 2611  78  68  -1 0.00
Sat 05/09 00Z 0.67 2612  78  44  -1 0.00
Sat 05/09 01Z 0.65 2712  77  29  -1 0.00
Sat 05/09 02Z 0.72 2713  77  19  -1 0.00
Sat 05/09 03Z 0.80 2713  70  15  -2 0.00
Sat 05/09 04Z 0.70 2711  64  19  -2 0.00
Sat 05/09 05Z 0.53 2710  57  31  -1 0.00
Sat 05/09 06Z 0.45 2610  49  30  -1 0.00
Sat 05/09 07Z 0.41 2510  46  19  -1 0.00
Sat 05/09 08Z 0.39 2510  45  17   0 0.00
Sat 05/09 09Z 0.33 2408  43  14   0 0.00
Sat 05/09 10Z 0.29 2207  42  26   0 0.00
Sat 05/09 11Z 0.20 2007  42  31   0 0.00
Sat 05/09 12Z 0.13 1809  44  36   0 0.00
Sat 05/09 13Z 0.08 1711  50  43   0 0.00
Sat 05/09 14Z 0.12 1712  58  63   0 0.00
Sat 05/09 15Z 0.30 1613  73  68   0 0.00
Sat 05/09 16Z 0.45 1714  87  89   0 0.02
Sat 05/09 17Z 0.14 1616  94  94   0 0.02
Sat 05/09 18Z 0.06 1615  96  93   1 0.02
Sat 05/09 19Z 0.07 1616  97  92   1 0.03
Sat 05/09 20Z 0.08 1717  97  90   2 0.03
Sat 05/09 21Z 0.07 1718  98  70   2 0.02
Sat 05/09 22Z 0.08 1717  98  69   3 0.02
Sat 05/09 23Z 0.09 1815  97  73   3 0.01
Sun 05/10 00Z 0.18 1916  98  73   3 0.01
Sun 05/10 01Z 0.27 2017  98  77   3 0.01
Sun 05/10 02Z 0.36 2119  98  56   4 0.01
Sun 05/10 03Z 0.40 2119  98  47   4 0.01
Sun 05/10 04Z 0.44 2120  98  29   4 0.01
Sun 05/10 05Z 0.49 2120  98  36   4 0.01
Sun 05/10 06Z 0.52 2221  97  38   4 0.01
Sun 05/10 07Z 0.51 2221  94  40   5 0.01
Sun 05/10 08Z 0.51 2222  93  61   5 0.01
Sun 05/10 09Z 0.50 2221  92  76   5 0.01
Sun 05/10 10Z 0.58 2322  96  89   5 0.01
Sun 05/10 11Z 0.64 2422  96  87   5 0.02
Sun 05/10 12Z 0.67 2422  96  84   4 0.01
Sun 05/10 13Z 0.76 2521  94  84   4 0.02
Sun 05/10 14Z 0.84 2519  89  53   3 0.01
Sun 05/10 15Z 1.07 2518  87  33   3 0.00
Sun 05/10 16Z 4.23 2416  93  23   3 0.01
Sun 05/10 17Z 3.04 2516  93  16   3 0.02
Sun 05/10 18Z 4.89 2515  83  18   3 0.02
Sun 05/10 19Z 9.74 2516  71  15   3 0.00
Sun 05/10 20Z 10.94 2515  67  14   4 0.00
Sun 05/10 21Z 11.20 2516  65  15   4 0.00
Sun 05/10 22Z 10.86 2518  63  13   3 0.00
Sun 05/10 23Z 5.60 2619  62  14   3 0.00
Mon 05/11 00Z 2.62 2720  59  22   2 0.00
Mon 05/11 01Z 1.58 2718  52  21   2 0.00
Mon 05/11 02Z 1.11 2818  44  20   1 0.00
Mon 05/11 03Z 0.75 2817  41  18   1 0.00
Mon 05/11 04Z 0.55 2916  51  19   0 0.00
Mon 05/11 05Z 0.43 3016  61  23   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