NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260411_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)
=== ===== === ==== ==== === === === ====
Sat 04/11 18Z 6.52 3016  85  15  -4 0.00
Sat 04/11 19Z 6.71 3018  81  13  -4 0.00
Sat 04/11 20Z 6.02 3118  79  13  -4 0.00
Sat 04/11 21Z 4.98 3119  76  13  -4 0.00
Sat 04/11 22Z 4.74 3120  74  10  -4 0.00
Sat 04/11 23Z 3.13 3222  75   8  -5 0.00
Sun 04/12 00Z 1.81 3224  78   7  -5 0.00
Sun 04/12 01Z 1.12 3225  80   8  -5 0.00
Sun 04/12 02Z 0.85 3226  78   9  -6 0.00
Sun 04/12 03Z 0.61 3227  75  10  -6 0.00
Sun 04/12 04Z 0.44 3326  71  11  -6 0.00
Sun 04/12 05Z 0.28 3324  67  10  -5 0.00
Sun 04/12 06Z 0.18 3322  64  10  -5 0.00
Sun 04/12 07Z 0.13 3420  64  11  -5 0.00
Sun 04/12 08Z 0.13 3317  65  14  -5 0.00
Sun 04/12 09Z 0.16 3316  65  18  -5 0.00
Sun 04/12 10Z 0.12 3314  62  19  -4 0.00
Sun 04/12 11Z 0.07 3312  57  23  -3 0.00
Sun 04/12 12Z 0.06 3310  52  27  -2 0.00
Sun 04/12 13Z 0.06 3207  47  32  -1 0.00
Sun 04/12 14Z 0.09 2904  45  31  -1 0.00
Sun 04/12 15Z 0.17 2504  47  25  -1 0.00
Sun 04/12 16Z 0.26 2305  47  24  -1 0.00
Sun 04/12 17Z 0.35 2105  46  36  -1 0.00
Sun 04/12 18Z 0.54 2006  45  34  -1 0.00
Sun 04/12 19Z 0.83 2008  44  29   0 0.00
Sun 04/12 20Z 0.45 1911  40  63   0 0.00
Sun 04/12 21Z 0.33 1912  40  93   0 0.00
Sun 04/12 22Z 0.16 1815  43  80   0 0.00
Sun 04/12 23Z 0.32 1920  49  92   0 0.00
Mon 04/13 00Z 0.39 1923  57  98   0 0.00
Mon 04/13 01Z 0.51 2026  66  98   1 0.01
Mon 04/13 02Z 0.49 2029  81  98   2 0.03
Mon 04/13 03Z 0.53 2132  82  98   3 0.02
Mon 04/13 04Z 0.51 2134  80  87   6 0.01
Mon 04/13 05Z 0.56 2237  86  86   7 0.00
Mon 04/13 06Z 0.59 2240  86  84   9 0.01
Mon 04/13 07Z 0.67 2343  88  70   9 0.00
Mon 04/13 08Z 0.75 2447  92  62  10 0.00
Mon 04/13 09Z 0.79 2447  92  50   9 0.01
Mon 04/13 10Z 0.81 2546  91  53   9 0.00
Mon 04/13 11Z 0.82 2546  91  67  10 0.01
Mon 04/13 12Z 0.83 2545  91  75   9 0.01
Mon 04/13 13Z 0.83 2542  93  74   9 0.01
Mon 04/13 14Z 0.83 2542  88  93   9 0.02
Mon 04/13 15Z 0.88 2443  90  95   9 0.02
Mon 04/13 16Z 0.99 2446  94  95   9 0.06
Mon 04/13 17Z 1.05 2445  96  94   9 0.08
Mon 04/13 18Z 1.07 2545  97  94   9 0.13
Mon 04/13 19Z 1.04 2542  97  91   9 0.11
Mon 04/13 20Z 1.02 2640  97  82   9 0.06
Mon 04/13 21Z 1.00 2639  97  61  10 0.04
Mon 04/13 22Z 1.00 2636  97  53   9 0.03
Mon 04/13 23Z 1.03 2735  98  46   9 0.03
Tue 04/14 00Z 1.10 2735  98  39   9 0.03
Tue 04/14 01Z 1.22 2737  97  31   9 0.02
Tue 04/14 02Z 1.27 2737  97  30   8 0.02
Tue 04/14 03Z 1.13 2836  96  29   8 0.02
Tue 04/14 04Z 0.99 2832  95  32   8 0.01
Tue 04/14 05Z 0.89 2930  96  33   8 0.01

Run total areal avg QPF for the Central_Greens is: 0.81 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