NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260826_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)
=== ===== === ==== ==== === === === ====
Wed 08/26 00Z 0.20 3007  86  86  10 0.00
Wed 08/26 01Z 0.26 3009  89  73  10 0.00
Wed 08/26 02Z 0.21 3109  90  60  10 0.00
Wed 08/26 03Z 0.16 3208  91  54  10 0.00
Wed 08/26 04Z 0.12 3208  92  52  10 0.00
Wed 08/26 05Z 0.12 3208  92  51  10 0.01
Wed 08/26 06Z 0.14 3209  91  50  10 0.02
Wed 08/26 07Z 0.13 3208  90  44  10 0.01
Wed 08/26 08Z 0.12 3107  89  41  10 0.00
Wed 08/26 09Z 0.15 3007  89  44  10 0.00
Wed 08/26 10Z 0.15 3007  87  43  10 0.00
Wed 08/26 11Z 0.14 3007  85  37  10 0.00
Wed 08/26 12Z 0.11 3106  84  33  10 0.00
Wed 08/26 13Z 0.08 3003  84  32  10 0.00
Wed 08/26 14Z 0.08 2802  87  28  10 0.00
Wed 08/26 15Z 0.08 2502  88  27  10 0.00
Wed 08/26 16Z 0.10 2502  89  28  10 0.00
Wed 08/26 17Z 0.14 2302  90  28  10 0.00
Wed 08/26 18Z 0.17 2202  89  27  10 0.00
Wed 08/26 19Z 0.22 2103  89  23  10 0.00
Wed 08/26 20Z 0.24 2104  89  20  10 0.00
Wed 08/26 21Z 0.23 2004  89  18  10 0.00
Wed 08/26 22Z 0.18 2005  89  12  10 0.00
Wed 08/26 23Z 0.22 2006  89   8  10 0.00
Thu 08/27 00Z 0.26 2108  87   5  10 0.00
Thu 08/27 01Z 0.26 2108  83   9  11 0.00
Thu 08/27 02Z 0.26 2110  80  13  11 0.00
Thu 08/27 03Z 0.28 2111  78  13  11 0.00
Thu 08/27 04Z 0.30 2112  76  12  11 0.00
Thu 08/27 05Z 0.38 2114  78  13  11 0.00
Thu 08/27 06Z 0.43 2215  81  13  11 0.00
Thu 08/27 07Z 0.47 2216  84  13  11 0.00
Thu 08/27 08Z 0.52 2217  84  11  11 0.00
Thu 08/27 09Z 0.53 2218  86  10  11 0.00
Thu 08/27 10Z 0.46 2118  83   9  12 0.00
Thu 08/27 11Z 0.43 2118  87  15  12 0.00
Thu 08/27 12Z 0.45 2120  92  67  12 0.00
Thu 08/27 13Z 0.50 2120  97  71  12 0.03
Thu 08/27 14Z 0.53 2121  98  62  12 0.02
Thu 08/27 15Z 0.56 2122  97  51  12 0.01
Thu 08/27 16Z 0.64 2022  97  35  12 0.00
Thu 08/27 17Z 0.66 2022  95  55  12 0.01
Thu 08/27 18Z 0.73 1922  93  45  12 0.00
Thu 08/27 19Z 1.07 1923  90  70  13 0.00
Thu 08/27 20Z 1.06 1924  89  60  13 0.00
Thu 08/27 21Z 0.82 1925  90  54  13 0.00
Thu 08/27 22Z 0.67 1924  91  69  13 0.00
Thu 08/27 23Z 0.70 2026  92  66  13 0.00
Fri 08/28 00Z 0.70 2028  90  61  13 0.00
Fri 08/28 01Z 0.57 2028  88  67  14 0.00
Fri 08/28 02Z 0.57 2030  91  60  14 0.00
Fri 08/28 03Z 0.62 2130  94  61  14 0.06
Fri 08/28 04Z 0.72 2130  98  68  13 0.05
Fri 08/28 05Z 0.81 2231  97  70  13 0.03
Fri 08/28 06Z 0.78 2229  93  72  13 0.03
Fri 08/28 07Z 0.62 2324  91  69  13 0.01
Fri 08/28 08Z 0.59 2321  95  68  13 0.01
Fri 08/28 09Z 0.55 2518  95  54  13 0.01
Fri 08/28 10Z 0.50 2617  94  36  12 0.01
Fri 08/28 11Z 0.43 2714  91  35  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.32 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