Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260626_0600
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 06/26 06Z 0.28 2020  87  97  11 0.00
Fri 06/26 07Z 0.33 2019  89  95  11 0.00
Fri 06/26 08Z 0.37 2119  93  88  10 0.00
Fri 06/26 09Z 0.34 2117  93  92  11 0.00
Fri 06/26 10Z 0.36 2118  97  92  11 0.02
Fri 06/26 11Z 0.39 2218  98  90  11 0.21
Fri 06/26 12Z 0.40 2217  98  86  11 0.08
Fri 06/26 13Z 0.42 2217  96  87  11 0.07
Fri 06/26 14Z 0.40 2215  98  75  11 0.07
Fri 06/26 15Z 0.40 2312  98  70  11 0.07
Fri 06/26 16Z 0.41 2411  96  78  11 0.01
Fri 06/26 17Z 0.42 2410  95  65  11 0.00
Fri 06/26 18Z 0.47 2309  94  54  11 0.00
Fri 06/26 19Z 0.50 2208  94  75  11 0.02
Fri 06/26 20Z 0.55 2509  87  73  12 0.34
Fri 06/26 21Z 0.53 2814  85  64  11 0.14
Fri 06/26 22Z 0.44 2914  85  50  11 0.03
Fri 06/26 23Z 0.37 3012  88  48  11 0.00
Sat 06/27 00Z 0.34 3012  91  50  11 0.01
Sat 06/27 01Z 0.24 3112  90  59  11 0.00
Sat 06/27 02Z 0.21 3110  90  52  11 0.00
Sat 06/27 03Z 0.22 3110  89  49  11 0.00
Sat 06/27 04Z 0.22 3110  87  46  11 0.00
Sat 06/27 05Z 0.27 3012  88  46  11 0.00
Sat 06/27 06Z 0.28 3013  88  48  11 0.00
Sat 06/27 07Z 0.31 3013  90  51  10 0.00
Sat 06/27 08Z 0.31 3013  92  56  10 0.00
Sat 06/27 09Z 0.29 3012  94  43  10 0.00
Sat 06/27 10Z 0.30 3013  94  48  10 0.00
Sat 06/27 11Z 0.28 3013  92  46  10 0.00
Sat 06/27 12Z 0.23 3112  90  47  10 0.00
Sat 06/27 13Z 0.19 3112  89  45  10 0.00
Sat 06/27 14Z 0.16 3211  89  45  10 0.00
Sat 06/27 15Z 0.14 3210  89  44  10 0.00
Sat 06/27 16Z 0.14 3208  89  46  10 0.00
Sat 06/27 17Z 0.16 3208  87  44  10 0.00
Sat 06/27 18Z 0.25 3208  85  43  10 0.00
Sat 06/27 19Z 0.24 3207  82  43  10 0.00
Sat 06/27 20Z 0.20 3307  80  41  10 0.00
Sat 06/27 21Z 0.16 3307  80  41  11 0.00
Sat 06/27 22Z 0.09 3306  80  38  11 0.00
Sat 06/27 23Z 0.06 3406  80  37  11 0.00
Sun 06/28 00Z 0.10 0006  80  38  11 0.00
Sun 06/28 01Z 0.05 0005  80  41  11 0.00
Sun 06/28 02Z 0.03 3506  79  40  11 0.00
Sun 06/28 03Z 0.06 0007  76  41  12 0.00
Sun 06/28 04Z 0.07 0106  74  41  12 0.00
Sun 06/28 05Z 0.08 0106  72  42  12 0.00
Sun 06/28 06Z 0.06 0105  69  42  12 0.00
Sun 06/28 07Z 0.06 0106  68  41  11 0.00
Sun 06/28 08Z 0.08 0107  67  39  11 0.00
Sun 06/28 09Z 0.08 0107  67  38  11 0.00
Sun 06/28 10Z 0.10 0108  65  33  11 0.00
Sun 06/28 11Z 0.10 0108  66  30  11 0.00
Sun 06/28 12Z 0.14 0210  67  28  11 0.00
Sun 06/28 13Z 0.18 0211  70  26  11 0.00
Sun 06/28 14Z 0.22 0311  73  24  11 0.00
Sun 06/28 15Z 0.22 0309  75  25  11 0.00
Sun 06/28 16Z 0.23 0306  76  25  10 0.00
Sun 06/28 17Z 0.62 0305  76  23  10 0.00

Run total areal avg QPF for the Central_Greens is: 1.07 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