NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260718_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 07/18 00Z 0.46 2705  55  13  12 0.00
Sat 07/18 01Z 0.56 2706  50  12  12 0.00
Sat 07/18 02Z 0.49 2606  47  11  12 0.00
Sat 07/18 03Z 0.46 2406  47   9  12 0.00
Sat 07/18 04Z 0.50 2308  49  10  12 0.00
Sat 07/18 05Z 0.51 2310  51  12  12 0.00
Sat 07/18 06Z 0.52 2311  53  22  12 0.00
Sat 07/18 07Z 0.47 2311  51  65  12 0.00
Sat 07/18 08Z 0.50 2312  48  83  12 0.00
Sat 07/18 09Z 0.48 2312  46  90  13 0.00
Sat 07/18 10Z 0.59 2414  44  97  12 0.00
Sat 07/18 11Z 0.46 2314  46  94  13 0.00
Sat 07/18 12Z 0.57 2119  53  85  13 0.00
Sat 07/18 13Z 0.69 2125  66  80  13 0.00
Sat 07/18 14Z 0.84 2128  73  70  14 0.00
Sat 07/18 15Z 0.90 2129  75  71  15 0.00
Sat 07/18 16Z 0.96 2128  66  66  16 0.00
Sat 07/18 17Z 1.92 2232  87  82  14 0.01
Sat 07/18 18Z 0.89 2132  95  91  14 0.01
Sat 07/18 19Z 0.85 2232  98  68  15 0.02
Sat 07/18 20Z 0.78 2230  98  71  16 0.03
Sat 07/18 21Z 0.73 2228  98  71  16 0.02
Sat 07/18 22Z 0.72 2227  97  65  16 0.01
Sat 07/18 23Z 0.65 2228  94  66  17 0.02
Sun 07/19 00Z 0.96 2336  91  63  17 0.02
Sun 07/19 01Z 0.67 2232  74  51  17 0.07
Sun 07/19 02Z 0.74 2232  87  40  16 0.00
Sun 07/19 03Z 0.85 2429  92  46  15 0.01
Sun 07/19 04Z 0.94 2629  94  52  14 0.04
Sun 07/19 05Z 0.95 2728  98  62  13 0.07
Sun 07/19 06Z 0.75 3027  97  43  11 0.04
Sun 07/19 07Z 0.53 3129  95  14  10 0.02
Sun 07/19 08Z 0.45 3231  93   9   9 0.01
Sun 07/19 09Z 0.35 3230  92   9   9 0.01
Sun 07/19 10Z 0.27 3230  90  10   9 0.01
Sun 07/19 11Z 0.23 3328  87  14   8 0.01
Sun 07/19 12Z 0.21 3327  89  18   8 0.00
Sun 07/19 13Z 0.28 3225  90  16   8 0.00
Sun 07/19 14Z 0.40 3224  90   9   7 0.00
Sun 07/19 15Z 0.68 3121  91   5   7 0.00
Sun 07/19 16Z 0.71 3119  89   8   7 0.00
Sun 07/19 17Z 2.20 3118  82  20   7 0.00
Sun 07/19 18Z 6.13 3117  73  27   8 0.00
Sun 07/19 19Z 8.69 3018  68  11   8 0.00
Sun 07/19 20Z 8.25 3019  68   3   8 0.00
Sun 07/19 21Z 8.87 3020  70   2   8 0.00
Sun 07/19 22Z 8.16 3020  73   6   8 0.00
Sun 07/19 23Z 3.34 3120  71   9   8 0.00
Mon 07/20 00Z 1.19 3121  66   8   8 0.00
Mon 07/20 01Z 0.95 3121  62  10   8 0.00
Mon 07/20 02Z 0.91 3122  60  12   8 0.00
Mon 07/20 03Z 0.78 3222  61  14   8 0.00
Mon 07/20 04Z 0.61 3221  64  16   8 0.00
Mon 07/20 05Z 0.53 3221  66  16   8 0.00
Mon 07/20 06Z 0.46 3219  65  19   8 0.00
Mon 07/20 07Z 0.40 3216  64  21   8 0.00
Mon 07/20 08Z 0.39 3214  65  26   8 0.00
Mon 07/20 09Z 0.36 3213  64  29   8 0.00
Mon 07/20 10Z 0.33 3113  63  32   8 0.00
Mon 07/20 11Z 0.30 3112  62  37   8 0.00

Run total areal avg QPF for the Central_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