NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260516_1800
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 05/16 18Z 2.23 2110  58  41   9 0.00
Sat 05/16 19Z 1.92 2113  57  34  10 0.00
Sat 05/16 20Z 2.62 2115  62  30  10 0.00
Sat 05/16 21Z 3.77 2219  69  43  10 0.00
Sat 05/16 22Z 2.97 2223  72  34  10 0.00
Sat 05/16 23Z 1.04 2223  73  36  10 0.00
Sun 05/17 00Z 0.87 2223  70  49  11 0.00
Sun 05/17 01Z 0.97 2326  73  89  11 0.01
Sun 05/17 02Z 0.84 2228  82  94  10 0.05
Sun 05/17 03Z 1.17 2334  88  93  10 0.09
Sun 05/17 04Z 1.24 2535  93  55  10 0.05
Sun 05/17 05Z 1.17 2633  97  29  10 0.03
Sun 05/17 06Z 1.07 2732  97  14  10 0.03
Sun 05/17 07Z 0.93 2832  91  12  10 0.02
Sun 05/17 08Z 0.81 2931  83  16  10 0.01
Sun 05/17 09Z 0.66 3028  71  29  10 0.01
Sun 05/17 10Z 0.59 3026  63  21  10 0.01
Sun 05/17 11Z 0.59 2926  55  36  10 0.00
Sun 05/17 12Z 0.63 2926  50  33  10 0.00
Sun 05/17 13Z 0.71 2927  50  37   9 0.00
Sun 05/17 14Z 0.82 2827  56  53   9 0.00
Sun 05/17 15Z 0.97 2925  62  50   8 0.01
Sun 05/17 16Z 3.29 2923  66  48   8 0.00
Sun 05/17 17Z 5.76 2921  69  36   8 0.00
Sun 05/17 18Z 5.92 2917  74  29   8 0.00
Sun 05/17 19Z 5.78 2916  74  29   8 0.00
Sun 05/17 20Z 4.37 3014  71  24   8 0.00
Sun 05/17 21Z 2.81 3013  70  24   8 0.00
Sun 05/17 22Z 1.00 3012  71  21   8 0.00
Sun 05/17 23Z 0.68 3113  72  20   8 0.00
Mon 05/18 00Z 0.53 3112  71  17   8 0.00
Mon 05/18 01Z 0.54 3013  72  18   8 0.00
Mon 05/18 02Z 0.43 3012  69  15   8 0.00
Mon 05/18 03Z 0.38 3012  67  13   8 0.00
Mon 05/18 04Z 0.34 2911  65  11   9 0.00
Mon 05/18 05Z 0.30 2911  62  13   9 0.00
Mon 05/18 06Z 0.26 2910  61  16  10 0.00
Mon 05/18 07Z 0.23 2909  58  17  10 0.00
Mon 05/18 08Z 0.22 2809  54  23  11 0.00
Mon 05/18 09Z 0.17 2707  53  40  11 0.00
Mon 05/18 10Z 0.16 2406  56  46  11 0.00
Mon 05/18 11Z 0.16 2208  60  43  11 0.00
Mon 05/18 12Z 0.16 2110  67  66  11 0.00
Mon 05/18 13Z 0.15 2111  73  88  11 0.00
Mon 05/18 14Z 0.15 2112  78  94  11 0.00
Mon 05/18 15Z 0.18 2014  84  76  12 0.00
Mon 05/18 16Z 0.18 2016  87  55  12 0.00
Mon 05/18 17Z 0.21 2019  91  47  12 0.00
Mon 05/18 18Z 0.28 2119  92  34  12 0.00
Mon 05/18 19Z 0.34 2120  90  23  13 0.00
Mon 05/18 20Z 0.36 2219  86  17  14 0.00
Mon 05/18 21Z 0.40 2218  87  10  14 0.00
Mon 05/18 22Z 0.42 2219  91  14  14 0.00
Mon 05/18 23Z 0.49 2222  92  16  15 0.01
Tue 05/19 00Z 0.50 2323  91  20  15 0.01
Tue 05/19 01Z 0.59 2426  90  22  16 0.01
Tue 05/19 02Z 0.67 2429  90  26  16 0.02
Tue 05/19 03Z 0.72 2431  87  29  17 0.02
Tue 05/19 04Z 0.82 2533  89  30  17 0.02
Tue 05/19 05Z 0.91 2534  89  29  16 0.02

Run total areal avg QPF for the greens is: 0.43 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